100% Merino Light


¥7,700 Tax included


Heavy Duty
Pure Merino Wool

Merino wool’s exceptional heat and humidity regulation, and naturally powerful deodorizing properties make it the ultimate material for active hiker wear.

The latest 2022 fabric is the updated version of our proprietary, washable and shrink-proof merino wool, being approximately 10% lighter with 150-155g/m2 in average weight. It is suitable and comfortable even in warm seasons.

Offers extreme comfort and ease of movement. Also recommended to wear it with the Yamatomichi Trail Shirt.

Spirality after the Wash

The fabric will be spirally twisted when it is wet, especially right after the wash. It will be untwisted and restored to a certain extent by the line-dry because of its own weight and downward gravity.  
The extent of spirality (twisting) differs in each product, and it can only be recognized after it has been washed and dried. Therefore, if the spirality, twisting, or distortion of the fabric is apparent after the purchase, we will accept a return and a full refund even after washing and wearing. However, if you wish to return it, please contact us within 10 business days after you receive the product.

Where Are Charcoal Marl and Gray Marl?

In some products in Charcoal Marl and Gray Marl colors, the extent of spirality exceeded our standard, and therefore, we categorize these two colors as “C” products and offer them at a 20% discount. The two colors are sold separately from other colors as “100% Merino Light Sleeveless C”.


Granite Green
Friar Brown
Blue Gray


Made in Akita, Japan

100% Merino Wool 150-155g/m2
103g (Size S)
113g (Size M)
122g (Size L)
134g (Size XL)
MEN | S / M / L / XL

Product Story 1

Love for Merino

Akira Natsume, Yamatomichi Founder

I really love Merino fabrics. They are almost odor-free even when I sweat, comfortable, and keep the humidity and temperature constant even if I get soaked. Merino wool has so many natural and excellent properties that make it perfect for hiking.

When thru-hiking over a longer period, I really start to feel that I myself am part of nature. It is like my body somehow resonates and links with the greatness of my surroundings.

Deep in the mountains, as I walk, run, sweat, sleep, wake up and walk again, Merino wool is always my choice. For me, it connects my body with nature, and that is why I continue to focus on items made of pure Merino wool without any added synthetic fibers.

I have spent so much time and money developing our proprietary merino fabric. Why? This is all because of my love for merino!

Naomi Kazama, wearing the Navy color.

Product Story 2

Spirality: Solution and Mechanism

By Rin Matsumoto and Takahiro Yamamoto

We have updated the 100% Merino Light fabric from the previous 165-170g/m2 to a lighter 150-155g/m2 fabric. In 2021, we achieved a major shift from ply-yarn to single yarn*, improving dimensional stability even after washing. As a result, we had fewer complaints from our customers about shrinkage, however, the earlier version was heavier than we expected and felt a little too hot in mid-summer.

*Single yarn is a single spun yarn, while ply-yarn is made by twisting two single yarns together.

We decided to further improve the 2021 version to create a lighter and more comfortable fabric even at high temperatures during the summer. The lighter fabric naturally doesn’t provide as much insulation, but for us the lighter the better. Read on to learn how we have updated the fabric.

Make It Lighter!

To lighten a fabric, there are two basic options:

  1. Make the yarn finer
  2. Loosen the knitting density

The 2021 version used a super fine wool yarn (grade 1/52), and any finer yarn would have been hard to come by and would have been lacking in strength. Hence we decided to explore reducing the weight by loosening the knitting density. This requires delicate adjustments to achieve a good balance of yarn thickness and knitting gauge. We decided to make three prototypes with three different density levels.
All three prototype fabrics were successfully lighter than the 2021 version. The lightest was 135g/m2, which was so lightweight that it was too thin and unreliable. The heaviest was 150g/m2, and it was the closest to the target weight we were aiming for. We decided to proceed with the development based on this 150/m2 prototype.
Our analysis showed that the 150g/m2 prototype fabric performed better in terms of air permeability but let out heat due to the looser density. While this result was expected, sadly, the tensile and burst strength also declined. The decrease in tensile and burst strength due to a looser weave is a physical disadvantage resulting from the weight reduction, but we thought it was essential to make the fabric as strong as possible.

Meeting after meeting with the development team of a fabric manufacturer in Bishu, we decided to increase the twist count of the yarn to make it stronger. Yarn with a high number of twists, or high-twist yarn is generally stronger and less likely to get fuzzy. In addition, we decided to increase the density of the 150g/m2 prototype to enhance the strength.

The next prototype fabric was made of a high-twist yarn with increased density. The weight was a little heavier than the first prototype due to increased density, but it seemed more stable and improved in many aspects. The tensile and burst strength, which was one of the most important factors, was also enhanced. In our test, the prototype performed well in dimensional stability after washing, bringing us closer to our ideal.

Next, to test the durability after washing and drying, we produced more prototypes for testing. After twenty consecutive cycles of both washing and tumble-drying at a low temperature, we confirmed that the prototypes performed well; they were in good shape and stable in measurements.

Spirality: Why and How It Occurred

After the favorable result of the prototype test, we started to get ready for production. We waited for the fabric to be finalized by the manufacturer, but oddly, they didn’t deliver it at the agreed date. We contacted the manufacturer, and they told us that they were trying to do their best to fix a problem of “spirality”.

Spirality is a fabric’s tendency of twisting toward a certain direction. If a spirality issue is noticeable in a T-shirt, it means that the shape of the T-shirt is distorted and twisted.

Usually, three factors can cause spirality: Using natural fibers, single yarn, and jersey knitting. Our fabric ticked all these boxes.

When we created the previous 2021 version fabric, we switched from ply-yarn to single yarn, in which we intentionally reversed the knitting direction so that it counteracts the yarn twists and neutralizes the spirality. This time, however, the twist count was increased to enhance yarn strength; it was probable that the yarn twist was so high that the twisting energy exceeded the knitted fabric’s untwisting tendency, thus the problem of spirality occurred.

We wanted a tumble-dryable fabric, which must have been a challenging demand for the manufacturer because the solution for the spirality issue was hard to find. The mechanism of spirality is as follows: When the wool fabric gets wet during washing and absorbs water, it swells, causing the high-twist yarns to untwist, thus spirality occurs. As the fabric dries, the spirality should be canceled and restored to its original shape. Still, the problem is that natural drying including line-drying and flat-drying is different from low-temperature tumble-drying in terms of the drying speed and the extent of untwisting. In other words, natural drying and tumble-drying remove the moisture of the shirt differently, thus it was impossible to achieve an equal balance of twisting and untwisting under both natural drying and tumble-drying.

“This same issue must have been an issue with the prototype too,” we thought. We checked the prototype again but didn’t find the same issue with spirality. Why? It was because we adjusted the balance of twisting and untwisting, focusing on low-temperature tumble-drying instead of line- or flat-drying. In mass production, on the contrary, the fabric manufacturer prioritized natural drying, so low-temperature tumble-drying caused the spirality issue.

If the “high-twist yarn” is causing the spirality issue, our attempts to improve the already knitted fabric will not lead us to a satisfactory solution. The fabric manufacturer did their best to improve the post-production, and the spirality was within the acceptable level of 2 to 3% in natural drying, which was below the generally acceptable standard for spirality of 5%. In low-temperature tumble drying, however, the spirality was unacceptable between 7 to 10%.

Should we label the product “Tumble-dry, low” or should we label it “Do not tumble-dry”? It was a difficult decision because the fabric scarcely shrunk and measurements were stable although the spirality was apparent. Consequently, we decided on “Do not tumble-dry” and recommended line-drying instead of flat-drying so that the fabric would smoothly untwist as it dries.

The degree of twisting and untwisting varies depending on how it is dried. The types of washing machines used are all different and sometimes it is washed in summer, sometimes in winter. We tested wool knitwear made by other companies on the market and concluded that the spirality issue is the fate of natural fibers such as cotton and wool to a more or less extent. We decided to sell the shirt made of this fabric since the spirality is not a disadvantage that affects the functionality or performance, but a characteristic of the fabric’s appearance.

Spirality has been unavoidable since we decided to adopt a stronger yarn. In this development, we realized that making something flawless in every aspect was difficult. In the endless journey of manufacturing, what’s important is the balance and priority of achievement. We are now moving on to the next stage of development, believing that the twists and turns will lead to even more sophisticated manufacturing.


Form and Function

Where the 100% Merino Light Stands

Though this product dries slower than general synthetic base layer T-shirts, it is less likely to cause hypothermia caused by the evaporation of sweat or other moisture. In other words, the new 100% Merino Light series focuses on moisture absorption rather than quick-drying, and on thermal insulation rather than cooling properties.

Recommended Scenes

When the temperature changes drastically
Wool is good at maintaining a constant temperature inside the garment, keeping you dry and comfortable even in situations where temperatures can suddenly change.

When worn under an outer shell
Synthetic base layers with low moisture absorption can feel very humid and stuffy. On the other hand, our 100% Merino’s superior moisture absorption properties, will help to keep you dry and comfortable when worn under an outer shell.

When worn for long hours
Synthetic clothes often become smelly relatively early on, even if they are deodorant finished. Wools, on the other hand, naturally eliminate odor when the fabric dries even after being soaked in sweat. This powerful anti-odor performance allows you to keep moving day after day, relatively comfortably without smelling too bad. For details, please visit HERE (Currently available in Japanese only).

When packing capacity is limited
Our Merino wool products can be worn in various situations for long hours without getting too smelly, minimizing the need for extra clothes in your backpack.

Yamatomichi Lab Base Layer Special Issue

In our base layer special issue, we highlight the outdoor base layer clothes. We analyze the materials and review the items of outdoor makers. It is currently available in Japanese only. For details, please visit the following link 『山と道ラボ ベースレイヤー編』.

Naturally Odor Resistant

Wool base layers are chosen by many hikers for the material’s excellent odor-neutralizing performance. Some say it’s almost odor-free even after a week of heavy hiking, but we’ll let you (and your friends) be the judge of that…

Wool’s deodorant mechanism is still a mystery. One theory has it that wool absorbs a large amount of odor-causing elements, and consequently, the odor is minimized to the level that cannot be detected by the sense of smell. We will conduct our own experiments and tests in the future.

Great Moisture Control

Wool is great to help you keep warm and cool as it naturally controls the moisture level within the clothes, always keeping you comfortable throughout the year.

Wool’s peculiar function is the benefit of the dead-air space between the crimped wool fibers, allowing for excellent breathability and moisture permeability. Furthermore, the cortex’s water absorption performance variably changes according to the humidity level of the outer air, that is, the higher the humidity outside, the more moisture it absorbs.

Even Warm When Wet

First, when wool absorbs moisture, the thermal phenomenon called “absorption heat” is generated. Secondly, its excellent insulation properties (low thermal conductivity) prevent the body heat from being lowered by evaporation. Also, the crimped fibers are bouncy and retain loft without crushing even when wet.
In addition, wool can absorb more moisture in between the fibers, always keeping the skin dry and comfortable.

Consequently, 100% Merino wool keeps you warm during the action, even in severe weather that makes you wet to the skin.

When fibers absorb moisture, the thermal phenomenon called “absorption heat” is generated. The wool’s adsorption heat performance is twenty times of polyester, and 2.5 times of cotton.


The collar and arm holes feature stretch-resistant bound stitching.

The neckband seam is reinforced with a binding finish, attaching a strip of fabric from both shoulders to the back of the neck to cover the seam.


More Durable and Stable Quality

We have focused on using 100% merino wool without synthetic fibers. However, pure merino often triggers caused a lack of strength, yarn breakage, and shrinkage after washing.

We examined the optimal spinning and knitting methods, and our conclusion was to work with single yarn. The fabric uses the high-twist yarn and is pre-shrunk by tumble drying, which is a rare process for merino clothes, making the fabric strong but bouncy.

Our proprietary fabric is produced in Bishu, the production area of wool garments in Japan, in cooperation with the spinning company, fabric factory, dyeing, and processing factory, and inspection organization. We continue our effort to innovate with new products and markets.

The fabric is thin and light. The light colors may be slightly transparent.

100% Merino Wool

Weight: 150-155g/m²
Yard count: 1/52
Bursting strength (JIS L1096A): 264kPa*
*The value of the pressure when the rubber membrane tears the fabric as the membrane is continuously pressurized.
Heat retention (JIS L1096A): 17%*
*Energy loss when the fabric is placed on the heat source.

Why 100% Merino?

Wool is a natural material with various unique features such as temperature/moisture control, thermal insulation, and is naturally odor-resistant. All are developed by sheep to survive the harsh environment over time.

Merino wool comes from merino sheep and compared to other kinds of wool, merino fiber is finer, softer, and less scratchy, and hence even suitable for making underwear and baselayers.

All wool, including merino wool, is cool in summer and warm in winter. It is warm even when it’s wet, and practically odor-free even after many hours of wear.

While many other manufacturers add synthetic fibers to strengthen their Merino fabrics, we wanted to stick with 100% Merino to maximize the natural benefits of pure merino wool. Our merino will keep you dry even when it’s hot and humid and comfortable no matter the climate.

The above chart shows the comparison of moisture content ratio of three types of fabrics in a humid and hot environment (up, 30˚C with 90% humidity) and a more comfortable environment (down, 20˚C with 65% humidity).

In a humid and hot environment, the fiber with superior moisture absorption keeps you dry and comfortable. On the other hand, in dry conditions, it is more comfortable when the fiber provides a certain level of moisture without excessively absorbing available humidity. The difference of the moisture content ratio in the above chart indicates the moisture control performance: the greater the value is, the better the fabric’s moisture control performance is, therefore the larger percentage means better comfort.

The 100% merino fabric, as shown above, has a 6.8% moisture ratio difference. This means that our merino material can effectively control the moisture compared to the other fabrics, keeping you dry when it’s hot and humid while supplying a moderate amount of moisture when the humidity is low.
This is the reason why the merino wool is known as “a natural air conditioner”.

Merino Wool

Wool is a natural material with various unique features such as temperature/moisture control, thermal insulation, and anti-odor performance; all of them were developed by sheep to survive the harsh environment over time.

Merino wool comes from merino sheep and compared to other kinds of wool, merino fiber is finer, softer, and less scratchy, and hence even suitable for making underwear.

All wools, including merino wool, are cool in summer and warm in winter. It is warm even when it’s wet, and practically odor-free even after many hours of wear.

Wool’s Structure

The wool’s fiber is composed of amino acid-based protein, just like human hair and skin. The surface is called the “scale”, which is similar to a fish scale, and the inner part is the “cortex”.
The cortex is composed of the ortho-cortex and para-cortex, each with different moisture absorption performances. Because each of them differs in property, the combination of ortho and para cortexes makes the fiber “crimped”.
This crimped structure produces the wool’s unique features such as moisture/temperature control property and thermal insulation performance, avoiding the coldness caused by sweat.


Disadvantages of Wool

As explained above, wool or merino wool has various features and functions, but it is not flawless.

  • Easily absorbs moisture and becomes heavy
    Wool can get quite heavy as it is great at absorbing moisture. This also means that wool takes longer to dry than synthetic fibers, but compared to cotton, it actually dries faster.
  • Liked by insects
    Soft, natural fibers such as wool, cashmere, and silk are prone to damage by insects.
  • Easily damaged
    The relatively short fibers of wool mean that wool fabrics are easier damaged than synthetic and cotton fibers. However, small holes can easily be fixed with a bit of pure wool and a needle.
  • Shrinks easily
    Wool generally shrinks easily, even when shrink-proofed. To reduce shrinkage, after the wash, please spread the shirt well to return to its original shape and gently iron it.
  • Distortion
    When knitted wool fabrics are washed, the material is likely to distort diagonally because the yarned fibers absorb water, swell, and tend to untwist. Consequently, the shape of the shirt may distort slightly with washing.
  • Distinctive smell
    The wool comes from sheep and you may experience a distinctive animal-like smell coming from your t-shirt when damp. This smell usually disappears after the fabric dries.

The above information was compiled and edited based on the interview with the textile company and the research institute, and the reference book below:

Structure and Physical Properties of Wool, Japan Wool Industry Association, Seni Co., Ltd.


  • Naomi 173cm-60kg
    Size L (Blue)

    • Naomi 173cm-60kg
      Size L (Blue)

      • Ken 169cm-55kg
        Size S (Charcoal Marl)

      • Ken 169cm-55kg
        Size M (Friar Brown)

      • Matsu 169cm-69kg
        Size M (Granite Green)

      • Matsu 169cm-69kg
        Size L (Navy)

      • Ippei 172cm-62kg
        Size M (Friar Brown)

      • Ippei 172cm-62kg
        Size L (Blue Gray)

      • Pony 173cm-76kg
        Size L (Navy)

      • Pony 173cm-76kg
        Size XL (Gray Marl)

      • Kim 175cm-70kg
        Size M (Mustard)

      • Kim 175cm-70kg
        Size L (Blue Gray)

      • Nacho 180cm-68kg
        Size L (Pale Yellow 2021)

      • Nacho 180cm-68kg
        Size XL (Navy)

        • Ken 169cm-55kg
          Size S (Charcoal Marl)

        • Ken 169cm-55kg
          Size M (Friar Brown)

        • Matsu 169cm-69kg
          Size M (Granite Green)

        • Matsu 169cm-69kg
          Size L (Navy)

        • Ippei 172cm-62kg
          Size M (Friar Brown)

        • Ippei 172cm-62kg
          Size L (Blue Gray)

        • Pony 173cm-76kg
          Size L (Navy)

        • Pony 173cm-76kg
          Size XL (Gray Marl)

        • Kim 175cm-70kg
          Size M (Mustard)

        • Kim 175cm-70kg
          Size L (Blue Gray)

        • Nacho 180cm-68kg
          Size L (Pale Yellow 2021)

        • Nacho 180cm-68kg
          Size XL (Navy)

          推奨サイズ / Recommended Size

          Size S M L XL
          体重 / Weight
          52~61 59~69 67~78 76~85
          胸囲 / Chest
          80~90 85~95 92~102 100~110

          製品サイズ / Product Size


          Unit: cm
          Size S M L XL
          着丈 / Length 66.5 69.5 71.5 73.5
          肩巾 / Shoulder Width 36.5 38.5 41.5 44.5
          身巾 / Body Width 45 47.5 51.5 55.5
          裾巾 / Hem Width 44 46.5 50.5 54.5

          The above values show the measurement when the item is brand-new and unwashed. After being washed and line-dried, it will be stretched vertically by 1 cm and shrunk horizontally by 1.5 cm from the listed values.
          – Due to the difference in the shrinkage tendency, there may be some individual differences in the measurements of the product.
          – Tumble-drying at low temperature may cause more shrinkage than when dried by natural drying. The shrunk item will be restored by washing and line-drying again.
          – Iron with steam if shrunk after the wash and drying. Gently stretch the fabric while ironing for the best results.

          Our 100% Merino Light series have a wide-fit, standard-fit, and slim-fit: 100% Merino
          Light Sleeveless is slim-fit.


          Color Transfer

          When the 100% Merino Light item in Blue, Mustard, or Navy is in contact with a white or light-colored shirt wet from rain or sweat, color may transfer and stain the shirt.


          The fabric will be spirally twisted when it is wet, especially right after the wash. It will be untwisted and restored to a certain extent*.

          *The extent of spirality (twisting) differs in each product


          Tumble-drying is NOT recommended for this item, as it may cause twisting and shrinkage. However, it can be tumble-dried at your own risk if you do not mind the spirality (twisting)*.

          *It will be untwisted and restored to a certain extent after it is washed again and line-dried.The tumble-drying may cause shrinkage and the length may be shortened by about 2-3cm, but it will be restored after washed again and line-dried.

          Care Instructions

          • This product is made of highly odor-resistant merino wool, which usually does not require a frequent wash.
          • The fabric uses shrink-proof pure merino wool. It is machine-washable by “Gentle Course” or “Hand Wash Course” with gentle water flow.
          • When you store the item, use mothballs and/or vacuum storage bags to keep out insects.
          • Merino’s fibers are short, and fuzz and pilling may appear, which can be removed by several washes.


          For more detailed tips on how to wash, store and restore the shrunk item, please visit the following link: How to Care the 100% Merino Series


          • We only accept payment by credit card. We currently do not accept payment via bank transfer from overseas accounts.
          • We accept the following Credit Cards: Visa, Master, American Express, and JCB.
          • To download your receipt, please click the link included in the Dispatch Notice, which we will send by email as soon as the items are dispatched.


          We will ship by DHL for overseas customers (excluding China, Hong Kong, Taiwan, Korea and Russia). For customers in China, Hong Kong, Taiwan, Korea and Russia, we will ship by EMS only. Shipping costs vary depending on your country and region.

          Size Exchange

          • Overseas customers who need to change the size of their order, should note that the time needed for shipping will vary greatly depending on your country of residence.
          • We only accept exchanges when the item is unused (except for fitting).
          • If you wish to exchange the size of the item, please contact us within seven days of receiving your order.
          • Exchanges can only be made for the same color in a different size.
          • If the size you wish is out of stock, we will suggest a different color.
          • If the product is out of stock, we may simply have to ship the item back to you.
          • All shipping costs to be carried by the customer.
          • We will only send the exchanged item to you, upon receipt of return shipping cost via PayPal.
          • Please be aware that some countries charge customs duties depending on the price of the item.
          • We are unable to answer any questions on local customs. Please contact your local customs bureau.


          A natural fiber, merino wool has wonderful properties such as excellent temperature and humidity control and deodorant performances, but it also has a weakness; yarns are likely to break and develop holes due to abusive use and moth eating.

          For inquiries on repairing holes or products damaged over time, please feel free to contact us from the “Repair” section of the SUPPORT page.

          Needle Felting

          Holes in merino wool cut-and-sewn products caused by thread breakage or moth bites can be repaired by felting, a technique to patch the hole with the raw wool using a special needle. You can repair by yourself, and Yamatomichi also offers felting repair services using raw wool of the same color as the product.

          For more details of felting and how we repair the merino items, visit Yamatomichi JOURNALS 『山と道修理部通信#1 メリノウールの穴を補修する』(Japanese only).