Yamatomichi Lab Special Issue; All-weather Activewear
#1 Air/Moisture-permeable Nanofiber

A nanofiber membrane is a air/moisture-permeable waterproof material that has a non-woven, mesh-like structure made from multiple layers of nano-level ultra-fine fibers (nanofibers). The manufacturing process of this type of membrane is called “electrospinning.”

In our past journals, we have largely classified waterproof and breathable fabrics into two categories: “hydrophilic non-porous membrane” and “hydrophobic porous membrane”. Nanofiber membranes, however, do not belong to either of these categories in terms of the manufacturing method and can be described as a third technology.

Before the in-depth discussion of nanofiber membrane, let me summarize all three waterproof/breathable technologies.

*Gore-tex has many variations, presumably including the non-coated version for better moisture-permeability.
**Polartec NeoShell’s mechanism is not disclosed by the manufacturer. We concluded that it is a nanofiber membrane based on its ventilating performance and the electron micrographs.

We once wrote “a hydrophilic non-porous membrane absorbs moisture like a towel, whereas a hydrophobic porous membrane works like a flexible mesh”, but as we have deepened our understanding towards nanofiber technology, we recognize that “a flexible mesh” was not the best metaphor. The porous membrane’s pores are not large enough for the air to pass through smoothly, consequently, its breathability is significantly inferior to that of nanofibers.

*cf. Yamatomichi Rainwear Journal No.6 (English not available)

Our in-house test showed that hydrophobic porous membranes can be categorized into two types: those with slight air permeability (*eVent and Gore-tex Shakedry) and those with no air permeability at all (Pertex Shield Pro). The reason for this was unknown, but now we can hypothetically conclude that the difference is caused by the characteristics of the fabrics.

*Results by KES method, in which high voltage is applied. In the Frazier method, a general breathability test, the air permeability of both eVent and Shakedry was not detectable.

Hydrophobic porous membranes are manufactured by stretching the polyurethane material to make a thin film. Polyurethane-based membranes, such as Pertex Shield Pro, are so elastic that the pores are stretched but not widened. On the other hand, the Teflon-based membranes with inferior elasticity such as eVent and Shakedry split here and there when stretched, and it looks like a nanofiber membrane under a microscope. Consequently, it is considered that the Teflon-based porous membranes have more clearances for the air to pass through, achieving moderate breathability.

*Results of the in-house tests at an inspection agency. Breathability is measured by the “JIS L 1096 Frazier method”, moisture-permeability by the “JIS L 1099A-1 method”, and water pressure resistance by the “JIS L 1092 B method (Kpa converted to mm)”. Values of moisture permeability and water pressure resistance are rounded off.　The sample materials may vary in quality and type. The results may differ depending on which part of the fabric was tested, so the values are for reference only.
**Catalog specs are based on the disclosed value by manufacturers. Please note that Gore-tex, Pertex, eVent, and NeoShell have many versions. Each version has different specs.
***Value after 5 times of washing.

Highly breathable nanofiber membranes are particularly suitable for intensive activities, such as trail running and fastpacking, where constant perspiration is expected.

However, many of the rainwear products intended for trail running and fastpacking focused only on keeping the weight low without too much concern regarding breathability. As a result, the term “breathability” may have mistakenly been considered interchangeable with “moisture-permeability”.

The forerunner of nanofiber, NeoShell, was announced 10 years ago in 2011. In 2019, The North Face announced a nanofiber fabric called Futurelight, which was advertised for its “breathability,” and suitability for high-intensity activities. Considering this, NeoShell is a very pioneering technology. With the release of Futurelight, NeoShell has once again come into the spotlight and perhaps the market is now more focused on “breathability.”

Although nanofiber membranes are suitable for high-impact activities, neither the current Neoshell nor the Futurelight are very lightweight fabrics. The weight of the jackets is in the mid 200g to 300g range, which is still heavy in today’s standards when products in the low 100g range exist.

Rainwear made with nanofiber membranes certainly has good breathability. However, their weight may interfere with mobility and they are often bulky. As a result, the final product is usually a relatively thick and heavy weatherproof jacket that is not very suitable for running. The thicker fabric also gives the impression that it is more likely to retain heat, which is not the impression you want with activities that require cooling down.

Also, the low water resistance is worth mentioning. The water pressure resistance of the NeoShell was said to be around 10000mm*, which is considered to be sufficient for most situations, but it is still relatively low compared to other technologies. We can only imagine the technical hurdle of making a fabric with a lot of porosity, to be thin and light without compromising its strength and being highly water-resistant.

*As shown in the above table, there are fabrics with higher water pressure resistance.

Pertex Shield Air is Pertex’s third waterproof and breathable nanofiber fabric, following Shield and Shield Pro.

The weight of the fabric is 50g/m2 to 60g/m2 (equivalent to the low to mid 100g range for a jacket), which is much lighter than conventional nanofiber fabrics. Pertex Shield Air is a ground-breaking fabric with good air permeability, high water resistance, and lightness that does not impair mobility.

When I asked the manufacturer why Shield Air was able to reduce the weight so much, the main reason was the combination with the ultra-light outer fabric, which is Pertex’s forte.

Nanofiber membranes have many pores, and although the membrane is usually thick, it is structured to be light (commonly about 0.02mm thick, but light as hydrophilic non-porous membranes that are about 0.007mm-0.01mm). However, combining the membrane with a lightweight outer fabric without sacrificing breathability and strength, which are what make nanofibers so special, requires a great deal of expertise. Pertex has been devoted to making ultra-lightweight materials for many years. Which is one of the reasons for their breakthrough in combining the two materials.

As a nanofiber, Pertex Sealed Air succeeded in significantly reducing weight, but more so, Pertex succeeded in keeping the quality of the membrane consistent.

Due to the manufacturing method and structure of nanofibers, variations in thickness and density are likely to occur, and thinner parts of the nanofibers have lower water pressure resistance. For this reason, companies either estimated the water pressure resistance at a conservative low level or did not disclose the value. In order to solve this problem, With Shield Air, Pertex focused on the consistency of the membrane, and succeeded in bringing the water pressure resistance to a guaranteed level while simultaneously balancing moisture permeability and breathability.

Previously, where lightweight nanofibers were non-existent, Shield Air is one of the first to successfully do so, and is also expected to bring great benefits in the harsh environments of fastpacking and running.

The following is a previous graph from “Rainwear #2” (English not available.) The graph maps out major fabrics in the market, arranged by situation/environment (vertical axis) and amount of exertion (horizontal axis), modified based on the latest product trends and subsequent studies.

In the graph we once envisioned, we categorized the ultra-lightweight jackets weighing less than 150 grams, as “waterproof windshells.”

In retrospect, this classification was mainly based on weight, and the listed products did not incorporate breathability and lightness, both characteristics windshells carry. Breathable fabrics such as Polartec NeoShell and Futurelight are most applicable, but never before have we seen such a simply designed product.

However, with the lightweight Pertex Shield Air joining the scene, we had no choice but to revise this graph. Until now, there wasn’t a product that could be categorized as a “waterproof windshell,” because they weren’t quite as breathable as windshells tend to be.

The Pertex Shield Air has made it possible to create an ultra-lightweight product that can be worn at all times, even during extremely strenuous activities, with the dexterity of a windshell and the weather resistance of rainwear. In other words, a literal “waterproof windshell” has finally been realized. This type of rain wear can be described as “All-weather Garments.”

Our UL All-weather series, using Pertex Sealed Air, scheduled to be released in June 2021, is named after this “all-weather” concept.

In the next article, #2, we will report on a simulated field pilot test with the Pertex Shield, Shield Pro, and Shield Air, which are made of three major waterproof/breathable technologies: hydrophilic non-porous, hydrophobic porous, and nanofiber, in a room under the same conditions.

To be continued in #2: Comparative Testing.