91g (Size S)
97g (Size M)
108g (Size L)
115g (Size XL)
- Introduction
- Yamatomichi’s first synthetic base layer
- Product story
- Why did we make a synthetic base layer?
- Form and function
- Say goodbye to sweat discomfort
- A synthetic that doesn’t smell
- Ammonia in base layers
- Lightweight and durable
- Wide fit, designed for comfort
- Details
- Review
- Product voice
- The story behind Chemical B
- Material
- Type EP by Teijin Frontier
- DELTAPEAK™ by Teijin Frontier
- Size guide
- Notes before use
- Differences in characteristics by color
- Residual odor
- Needle marks from production
- Instructions
- Care instructions
- Repair
Introduction
Yamatomichi’s first synthetic base layer
Co-developed with Teijin Frontier, the Chemical B Series eliminates two long-standing weaknesses of synthetic base layers: the chill from sweat and unpleasant odor.
Its point-contact knit structure quickly absorbs and dries sweat, reducing chill, while the slightly acidic yarn helps prevent the growth of bacteria that cause odor. The result is a synthetic base layer that brings together the best qualities of synthetics and merino wool.
With its roomy fit and simple design, Chemical B feels light and comfortable, lifting easily from the skin thanks to its point-contact structure. It’s designed for those who have avoided synthetic base layers in the past.
- Excellent moisture management for lasting comfort, even during long, high-intensity activity
- Outstanding odor resistance, despite being synthetic
- Lighter than merino wool
- Durable against pilling, even with its thin mesh fabric
Product story
Why did we make a synthetic base layer?
After years devoted to merino wool, why take on the challenge of creating a synthetic base layer?
To explore that question, I launched a year-long experiment called Yamatomichi Lab: Base Layer Edition (2019–2020). The aim was to better understand what makes a base layer truly perform. At the same time, I wanted to put merino wool through rigorous testing, confirm its strengths, and find a clearer way to share its unique appeal.
Special Roundtable: Tomoya Tsuchiya (Hiker’s Depot) × Kei Kuwahara (Run boys! Run girls!) × Yamatomichi Lab
What is a base layer? — An exploration taking historical developments into account
Natural Materials and Synthetic Fibers
What Is Insulation?
Comprehensive Evaluation of Base Layer Materials
Market Overview & Hands-on Reviews of Notable Products
Special Roundtable: Tomoya Tsuchiya (Hiker’s Depot) × Kei Kuwahara (Run boys! Run girls!) × Yamatomichi Lab
What is a base layer? — An exploration taking historical developments into account
Natural Materials and Synthetic Fibers
What Is Insulation?
Comprehensive Evaluation of Base Layer Materials
Market Overview & Hands-on Reviews of Notable Products
(Currently only available in Japanese)
Through countless comparative tests, we confirmed merino’s strengths—its odor resistance, temperature control, and moisture regulation. But I also came to appreciate what synthetics offer, especially their breathability and quick-drying performance.
From there, a new idea began to take shape:
- A synthetic base layer that resists odor like wool
- Yet is lighter and more durable, addressing wool’s weaknesses
This became the starting point of the project.
We found that odor control and insulation are especially important for hiking, while moisture-wicking, dispersing, and quick-drying properties are crucial for trail running.
We also identified two main approaches to managing sweat effectively:
Ventilation type — uses lightweight fabrics with mesh or grid structures to maximize breathability and speed up evaporation.
Wicking type — pulls sweat quickly away from the skin, spreads it across the fabric surface, and keeps the inside dry.
In other words, an excellent base layer needs three things: odor control, insulation (which doesn’t necessarily mean warmth), and superior sweat management. Of these, sweat management is the critical factor for both hiking and trail running.
The first two years of development were slow. As someone deeply attached to merino wool, I found it difficult to discover a synthetic material I truly wanted to wear while hiking.
Things changed once we began working with Teijin Frontier. Their trial fabrics treated with EcoPure®—a yarn treatment that suppresses odor-causing bacteria—showed impressive odor-eliminating performance. That discovery gave the project real momentum and accelerated development.
With EcoPure® providing reliable odor control, we concluded that the wicking approach—keeping the skin consistently dry—delivers greater comfort. Mesh fabrics work well for hot-weather trail running, but we found them less effective in cases of heavy sweating or in Japan’s hot, humid climate, where drying simply can’t keep up.
We tested countless prototypes. The first hurdle was odor control, followed by sweat management, and then durability.
As a brand that has long championed the strengths of merino wool, Yamatomichi could not settle for a half-hearted synthetic base layer. Our goal was to create one that hikers would actively choose even over merino. With that conviction, we pressed forward with development.
After overcoming each challenge, the final step was validation. Because sweat and body odor differ from person to person, a meaningful test required a diverse group of users. For this prototype, we involved 14 participants—including staff and partners—the largest test group we had ever assembled.
The research that began with Yamatomichi Lab: Base Layer Edition finally came together after five years in the form of Chemical B.
Feedback was largely positive, but it also revealed how differently people perceive odor control. Some felt Chemical B’s deodorizing effect was very strong, while others noticed it less.
To explore this, we measured the acidity and alkalinity of over 100 sweat samples using litmus paper, yet no clear pattern emerged.
What we did learn is that Chemical B is particularly effective at suppressing the ammonia odor that occurs immediately after exercise. However, it is less effective against acidic odor compounds such as butyric acid and isovaleric acid, which are commonly associated with body odor. Since sweat composition and body chemistry vary from person to person, this likely explains the range of experiences—a mystery we are eager to continue investigating.
At Takeda no Mori, December 2023 — my first and last trail running race (Photo: Ryo Hirano)
No matter how much data or how many test results we collect, what truly matters is how a product feels when you put it on and start moving.
For me, the real value of Chemical B isn’t only its odor control, but the comfort of its sweat management. Even when damp, it doesn’t cling to the skin or cause discomfort—and in this respect, I believe it even surpasses merino wool. On hot, demanding days, Chemical B is the base layer I instinctively reach for.
Form and function
Say goodbye to sweat discomfort
With its high breathability and fast-drying performance, Chemical B’s point-contact structure prevents the fabric from sticking to your skin, even when wet. It wicks moisture away like a sponge, drawing it to the outer surface and releasing it efficiently through a breathable mesh layer for rapid evaporation.
Conventional vs. Chemical B: moisture absorption and fast-drying performance
The chart below compares the quick-drying (left axis) and absorption (right axis) performance of base layers. The further left, the slower the drying; the further right, the slower the absorption. Chemical B stands out with an absorption time of just one second, showing its exceptional ability to instantly draw in sweat and disperse it.
Quick-Drying: Moisture content measured 15 minutes after dehydration of a fully saturated sample (a higher value indicates higher moisture content = lower quick-drying performance).
Moisture Absorption (JIS L 1907; Droplet Method): The time it takes for a single drop of water placed on the fabric to be fully absorbed.
A synthetic that doesn’t smell
Synthetic base layer fabrics excel in quick-drying and sweat management, but they have one major weakness: they tend to smell easily with sweat. Many manufacturers apply antibacterial, deodorizing, or odor-control treatments, but none have matched the natural deodorizing power of merino wool—a key reason Yamatomichi has long been committed to merino.
To address this, Yamatomichi partnered with Teijin Frontier to develop a synthetic fabric with advanced odor resistance. By using weakly acidic yarns that make it harder for odor-causing bacteria to thrive, and combining them with a quick-drying fabric structure, we created a material that stays fresher for longer.
While odor resistance was the original focus, our in-house tests also confirmed deodorizing effects—not complete, but noticeable. What’s more, these effects remain unchanged even after 100 washes.*
*Based on in-house testing at Yamatomichi
Ammonia in base layers
In Yamatomichi’s in-house tests, Chemical B did not quite match merino wool in deodorizing performance, but it far outperformed conventional synthetics with standard odor-control treatments. Moreover, since this test measured deodorization of odors that had already formed, there were also cases in real-world use where Chemical B surpassed wool by preventing odor from developing in the first place.
*Not fully effective against accumulated odors such as body odor that develops over time. For details, please see the Notes at the bottom of this page.
Lightweight and durable
Many synthetic base layer fabrics with excellent sweat management rely on mesh structures or ultra-lightweight materials, which often compromises durability. Achieving both performance and strength suitable for hiking gear has long been a challenge.
Chemical B addresses this with a special knitting technique that tightly weaves high-crimp yarns, making the fabric far less prone to pilling or snagging, even with the friction from backpack shoulder straps or hip belts. By carefully refining the fabric structure, we achieved an exceptional balance of lightness and durability.
*Because of its thin mesh construction, the fabric may still show wear depending on use conditions.
Wide fit, designed for comfort
Most synthetic base layers are designed with a tight, athletic fit in pursuit of performance. The Chemical B Pocket T-shirt takes a different approach, adopting a simple wide-fit pattern. Combined with the fabric’s volume and texture, it avoids looking overly sporty and works as a versatile synthetic base layer for a variety of situations.
Details
The wide neckline allows for ventilation and is finished with double layer binding for a clean, refined look.
Chest pocket for small essentials while hiking.
Small Yamatomichi brand tag placed at the right hem on the back.
Review
During development, 14 staff and friends tested prototypes and shared their feedback. Here, we highlight impressions from long journeys such as thru-hikes and endurance races.
On more demanding mountain days, I’d wear nothing else.
I think this might be Yamatomichi’s first product with a truly race-oriented style. In terms of lightness, quick-drying, and packability, it holds its own against products marketed by other brands for running and trail running—and honestly, I’d rather choose this one. I also use Yamatomichi’s 100% Light Merino for running, but for higher-output hikes and runs, I’d switch entirely to Chemical B.
I wore the Chemical B Sleeveless for long distances during the 2024 TJAR (Trans Japan Alps Race), and it was all I needed. Even after the race, the fabric showed no damage, fraying, or noticeable pilling. Since the fabric has limited stretch, I personally find it more comfortable to size up for better mobility.
TJAR 2024 competitor
Nicknamed “Popcorn,” Daisuke is an indoorsy type who loves anime, manga, and games. He’d rather not leave the house, but hiking helps him just barely avoid becoming a full-on shut-in. After years of moving around overseas for work, he gained weight and started running to lose it (and to enjoy good beer). Before he knew it, he had completed five traverses across Japan. He still hates running, and rebound weight gain is his constant companion.
22 days straight on the trail
I wore the Chemical B Sleeveless on a 600 km thru-hike across Iceland—and didn’t take it off for 22 days straight. Carrying 20 days’ worth of food and full camping gear, this single base layer stayed on day and night, for both hiking and sleeping.
Back in Japan, I decided to keep going and ended up wearing it for 30 days without a single change. By the very end there was some odor, but never that sharp, unpleasant “synthetic smell.” In fact, many days I caught myself thinking, “Wait—maybe it doesn’t smell at all?” Personal impressions aside, one thing was clear: even over long-term use, Chemical B showed outstanding odor resistance.
It also resisted chill after sweating, never felt sticky even when soaked, and unlike merino wool, I didn’t have to worry about abrasion.
For someone who used to choose only merino wool for base layers, Chemical B gave me a completely new option.
Yamatomichi Kamakura Staff
Originally from Osaka, Oji relocated to Kamakura in 2017. After working as a book planner and editor at an art-related publishing company he went freelance and now also works at our Yamatomichi Zaimokuza shop while running his own book business. He is also a keen gardener and hunter!
So odor-free it makes you wonder when the smell will come.
It doesn’t match merino completely, but compared to any synthetic I’ve worn, the difference was remarkable. Even with my heavy sweating, the fabric never felt soaked, heavy, or clammy—and it didn’t have that plasticky synthetic feel.
I wore it day and night for 14 days in the Swiss Alps (17–25°C during the day, 5–10°C at night) without a change. I sweated heavily every day, but odor didn’t appear until day 7, limited to the lower back where the pack pressed. The front and underarms stayed fresh the whole time, and even by day 13, only the back smelled enough to wash.
For a long trail, having one shirt that lasts is amazing. No changes, no laundry—just simple, comfortable days. With a base layer this odor-resistant, quick-drying, and comfortable, it’s the one I’d keep reaching for.
Yamatomichi Kyoto Staff
Ayana loved traveling since her student days and embarked on backpacking trips in search of nature. She developed a passion for hiking during these travels and began hiking while working as a nurse. She decided to quit her job to embark on overseas trekking adventures, exploring trails like the John Muir Trail in the US and trekking in Patagonia, Chile, Canada and South America. Through these adventures she was able to rediscover the beauty of Japanese mountains. After returning home, Ayana joined Yamatomichi as a staff in our Kyoto store. She enjoys trail running and is grateful for every minute spent in the mountains.
Beyond what you’d expect from synthetic
Last summer, I wore Chemical B on a thru-hike from sea level on the Japan Sea, across the Northern Alps, finishing at the summit of Mt. Fuji.
Even after a full week without changing, odor was never an issue—I simply thought, “Amazing for a synthetic!” The quick-drying performance was also a big plus: on a long journey, I could wash it, hang it up, and it would be dry in no time. Merino wool is often praised for not feeling cold when wet, but in reality it still clings to the skin and draws down body temperature. Chemical B, on the other hand, stayed off the skin even when damp, and dried so quickly that I felt completely at ease.
After reaching Mt. Fuji, I continued straight onto the Michinoku Coastal Trail. Since that trail connects mountains with towns, there are many points where you drop down into villages. Thanks to Chemical B’s excellent odor resistance, I could step into town with confidence, even after days on the trail.
Yamatomichi Kyoto Staff
Originally captivated by the allure of traveling abroad, a chance encounter during a trip ignited Daisuke’s passion for outdoor culture. This led to unforgettable experiences, including canoe touring in Canada and trekking in Alaska. Driven by a desire for longer, more immersive adventures, Daisuke tackled the Pacific Crest Trail (PCT) in North America in 2022, followed by the Continental Divide Trail (CDT) and Spain’s Camino de Santiago in 2023. Inspired by the ultralight hiking culture he encountered along the way, he joined Yamatomichi, eager to share these experiences with others. Always in pursuit of “a journey that feels true to himself,” he continues to explore and refine new styles of travel.
Product voice
The story behind Chemical B
The Chemical B Series is a base layer designed to eliminate sweat discomfort and odor while offering comfort, lightness, and durability. By combining the strengths of synthetics and merino wool, it achieves performance at a level we had long been striving for.
In this two-part video series—Overview and Behind the Scenes—Yamatomichi founder Akira Natsume and researcher Takahiro Watanabe share Chemical B’s features and performance, as well as the five-plus years of trial and error that went into its development.
Material
A proprietary Yamatomichi fabric that combines Teijin Frontier’s antibacterial pH-control material, Type EP—designed to maintain a mildly acidic balance—with their high-performance knit, DELTAPEAK™. The result is a breathable, sweat-resistant mesh with a point-contact structure.
The point-contact design lifts the fabric slightly from the skin, reducing cling and enhancing comfort. At the same time, the knit quickly absorbs sweat, spreads it across the surface, and releases it through the mesh for rapid evaporation. This combination of breathability and quick-drying performance keeps skin dry, comfortable, and free from stickiness.
By preventing moisture from returning to the skin, it also avoids the clammy chill typical of synthetic base layers, helping you stay comfortable even during breaks or in bad weather.
295kPa：Off White
*The above data is based on our in-house test results (measured values, not guaranteed values).
*Values shown are averages for each color (individual differences may exist within the same color).
Type EP by Teijin Frontier
With pH control technology, the fabric surface resists becoming alkaline, an environment in which odor-causing bacteria tend to thrive, and instead stays in a mildly acidic state that supports freshness. The fibers also become hydrophilic, allowing dirt to wash out more easily and preventing sebum buildup, which helps keep the product clean and easy to care for. Tests show that Type EP remains effective even after 100 washes*.
*Based on Yamatomichi’s in-house test results
DELTAPEAK™ by Teijin Frontier
A knitted fabric made from densely woven yarns with fine crimp (waviness), achieving an exceptionally smooth surface structure. The soft, highly stretchable material resists pilling and snagging while combining excellent absorbency with fast-drying performance. Despite being lightweight, the fabric is not see-through and also provides UV protection.
Cross Section (Image courtesy of Teijin Frontier co., Ltd)
Size guide
Size chart
| Size | XS | S | M | L | XL |
|---|---|---|---|---|---|
| Weight (kg) | 42~53 | 51~61 | 59~69 | 67~78 | 76~85 |
| Chest (cm) | 78~84 | 80~88 | 84~95 | 92~102 | 100~110 |
Product dimensions
Unit: cm
| Size | XS | S | M | L | XL |
|---|---|---|---|---|---|
| Length | 61 | 64.5 | 67.5 | 69.5 | 71.5 |
| Shoulder width | 38 | 41 | 43 | 46 | 48 |
| Body width | 47.5 | 52.5 | 55 | 59 | 62 |
| Hem width | 46.5 | 51.5 | 54 | 58 | 51 |
| Sleeve length | 19.5 | 21 | 22 | 23 | 24 |
| Sleeve opening | 16 | 17 | 17.5 | 18.5 | 19 |
Shrinkage from washing may vary between products, and can also be affected by the type of washing machine and course settings used.
Yamatomichi’s Chemical B series comes in Wide Fit, Standard Fit, and Slim Fit, and the Chemical B Pocket T-shirt is Wide Fit.
FItting
Oji 176cm 60kg
Size L (Navy)
Oji 176cm 60kg
Size L (Navy)
Shiori 167cm 55kg
Size S (Night Blue)
Shiori 167cm 55kg
Size S (Night Blue)
Makoto 166cm 55kg
Size S (Mustard)
Makoto 166cm 55kg
Size M (Navy)
Atsushi 169cm 54kg
Size S (Off White)
Atsushi 169cm 54kg
Size M (Night Blue)
Takuya 170cm 58kg
Size S (Mustard)
Takuya 170cm 58kg
Size M (Navy)
Oji 176cm 60kg
Size M (Olive)
Oji 176cm 60kg
Size L (Navy)
Seiichi 177cm 73kg
Size L (Mustard)
Seiichi 177cm 73kg
Size XL (Olive)
Ryota 185cm 70kg
Size L (Navy)
Ryota 185cm 70kg
Size XL (Off White)
Kenken 183cm 77kg
Size L (Navy)
Kenken 183cm 77kg
Size XL (Night Blue)
Makoto 166cm 55kg
Size S (Mustard)
Makoto 166cm 55kg
Size M (Navy)
Atsushi 169cm 54kg
Size S (Off White)
Atsushi 169cm 54kg
Size M (Night Blue)
Takuya 170cm 58kg
Size S (Mustard)
Takuya 170cm 58kg
Size M (Navy)
Oji 176cm 60kg
Size M (Olive)
Oji 176cm 60kg
Size L (Navy)
Seiichi 177cm 73kg
Size L (Mustard)
Seiichi 177cm 73kg
Size XL (Olive)
Ryota 185cm 70kg
Size L (Navy)
Ryota 185cm 70kg
Size XL (Off White)
Kenken 183cm 77kg
Size L (Navy)
Kenken 183cm 77kg
Size XL (Night Blue)
Kotone 153cm 44kg
Size XS (Night Blue)
Kotone 153cm 44kg
Size S (Mustard)
Saki 156cm 48kg
Size XS (Night Blue)
Saki 156cm 48kg
Size S (Off White)
Miho 159cm 51kg
Size XS (Night Blue)
Miho 159cm 51kg
Size S (Mustard)
Haruka 163cm 51kg
Size S (Off White)
Haruka 163cm 51kg
Size M (Olive)
Shiori 167cm 55kg
Size S (Mustard)
Shiori 167cm 55kg
Size M (Navy)
Kotone 153cm 44kg
Size XS (Night Blue)
Kotone 153cm 44kg
Size S (Mustard)
Saki 156cm 48kg
Size XS (Night Blue)
Saki 156cm 48kg
Size S (Off White)
Miho 159cm 51kg
Size XS (Night Blue)
Miho 159cm 51kg
Size S (Mustard)
Haruka 163cm 51kg
Size S (Off White)
Haruka 163cm 51kg
Size M (Olive)
Shiori 167cm 55kg
Size S (Mustard)
Shiori 167cm 55kg
Size M (Navy)
Notes before use
Differences in characteristics by color
- Due to differences in dye concentration, there are variations in how the functional properties from processing appear. Off White has slightly lower fabric strength compared to other colors, but on the other hand, it tends to show relatively higher antibacterial performance.
- Because of the fabric’s unique heathered texture, even the same color may appear slightly different in shade.
Residual odor
When wearing the Chemical B Pocket T-shirt previously used by another person, odors such as body odor may be noticeable. This is likely due to unfamiliar odors being absorbed into the fabric and perceived as unpleasant. In some cases, a moss-like smell has also been noted after immersion in rivers or streams.
The antibacterial and deodorizing performance of Chemical B may be reduced under the following conditions:
- Excessive buildup of sebum
- Increased alkalinity of sweat after perspiration
- Residues of alkaline detergents or chemicals remaining in the fabric
- Growth of acidic odor compounds (e.g., butyric acid, isovaleric acid—body odors produced by natural skin bacteria), such as when damp products are left unattended
Needle marks from production
Due to the characteristics of the fabric, sewing marks may remain from production, and small pinholes may become visible when the stitched areas are pulled. These pinholes do not weaken the fabric or affect its functionality. Products with more noticeable marks, however, will be offered at a reduced price in our Special Offer shop category.
Instructions
Care instructions
- Wash with a neutral detergent at a water temperature below 40°C.
- Hang dry in the shade.
- Do not use a dryer or iron, as heat can reduce the antibacterial and deodorizing properties.
- Avoid dry cleaning, fabric softeners, and bleach, as they can diminish the antibacterial and deodorizing performance.
Care instruction page
For more detailed washing, drying and water repellent care instructions, visit our SUPPORT Page. With proper care you can prolong the funtionality of the product.
Payment
- 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.
- Bank transfer is only availble for those that own a Japanese bank account.
Delivery
- Order Confirmation will be sent after the order.
- The items will be dispatched within 3 days after the payment is confirmed.
- The dispatch notice will be sent by email as soon as the items are dispatched.
- The delivery may be delayed by unforeseeable reasons such as natural disasters and other logistics issues. We appreciate your patience and understanding.
- We cannot ship multiple orders in one package due to how our delivery system is currently set up.
- We will ship to regions in North America, Oceania, and Europe (excluding Russia) via DHL. For regions in Asia, the Middle East, Central and South America, Africa, and Russia, we use EMS (International Express Mail Service) for shipping.
- Shipping fees and delivery times vary depending on the shipping destination as well as the size and weight of the items.
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.
Repair
We accept repairs for all of our Yamatomichi products. For inquiries on repair services including patching the holes, repairing with extra components, or fixing the items damaged over time, please feel free to contact us from the “Repair” section of the SUPPORT page.