Initial Report:
Zyflex Thermal Shirt And Pants

Product Information Manufacturer: Zyflex Manufacturer Website: http://www.zyflex.com/ Products Tested: Thermal Shirt and Thermal Pants Year of Manufacture: 2006 Color: Gray Sizes Available: Shirt is available in unisex youth S, M, L; and unisex adult S, M, L, XL, XXL. Pants are available in men’s and women’s S, M, L, XL, and men's XXL Size Tested: Shirt is XL, pants are men’s L Weight: Listed weights are 7 oz (198 g) for the shirt and  6.6 oz (187 g) for the pants; measured weights for the sizes tested are 8.9 oz (252 g) for the shirt and 6.9 oz (196 g) for the pants MSRP: Shirt is $34.99 US, pants is $29.99 US
	Zyflex Thermal Shirt and Pants (Photos from Zyflex website)

Product Description
From the manufacturer’s website:

"The Zyflex® Thermal Shirt provides superior warmth for its weight and is perfect for any winter activity. Comprised of our patented, breathable, water-resistant material, this shirt is a must for any outdoor adventure in adverse conditions. The shirt is constructed with raglan sleeves, an extended back, and external tags for optimal comfort and performance.”

"The Zyflex® Thermal Pants are designed to provide maximum insulation during the winter months. Comprised of our patented breathable fabric, the Zyflex pants will allow you to wear fewer layers and still be plenty warm in the harshest conditions. Designed with a soft elastic waistband and thin cuffs at the ankle.”

Initial Impressions.
The fabric used in the Zyflex Thermals is very unusual. It has a very fine grid pattern and a lot of horizontal stretch (with very little vertical stretch). The fabric is a medium weight and is slightly rough on both sides.

Since it has little pile (like fleece) to trap air, I don’t understand where its warmth is going to come from. Perusing Zyflex’s website, here is their claim on how the thermal garments work: “The secret of our performance lies in our patented construction. Insulation has been accepted to be directly proportional to the amount of entrapped air and is, therefore, proportional to fabric thickness. This has spawned a generation of bulky thermal wear that constricts an athlete's freedom to move in colder conditions. Zyflex® Thermal Sportgear incorporates new ultra microfibers that are held in place by continuous strands on nylon and spandex. Our composite fabric is designed to move with the athlete while preserving a greater amount of entrapped air than traditional fabrics of equal thickness.” Obviously it will require some testing under cold field conditions to find out if the garments work as claimed.

Looking at the label, the fabric composition is 59% polyethylene (not polyester), 35% nylon, and 6% Spandex. With 35% nylon, the fabric should certainly be durable. It’s also noteworthy that the fabric is claimed to be highly breathable AND water-resistant.

Test Plan
Test Period—Late May 2006 to late September 2006.

Test Locations—For the remainder of the spring I will be backpacking weekly in the mid elevation forested zone near my home in Colorado. This summer I will be backpacking weekly in the high alpine zone of the Colorado Mountains.

Testing Conditions—The testing environments will consist of forests and high elevation alpine country. Expected extreme conditions include: snow showers, strong winds, rain storms, heavy rain, intense sun, low temperatures, and high elevations with strong UV and intense thunderstorms. Terrains will be forest trails, off-trail bushwhacking, scrambling, and walking in rain and snow. Elevations will range from 6,000 to 13,500 ft (1829 to 4115 m) and expected nighttime temperatures will range from 20 to 55 F (-7 to 13 C).

How The Zyflex Thermals Will Be Used—Because of the late spring and summer testing situation, the Zyflex Thermals will be used for mountain backpacking and worn in camp and in my sleeping bag, where extra warmth is needed.

Measurements And Data—On each trip I will record the following data in relation to my comfort in the Zyflex Thermals: 1) temperature, 2) estimated wind speed, 3) estimated humidity, 4) altitude, 5) precipitation (including what form), 6) clothing or sleeping system the Zyflex Thermals was used with 7) clothing worn over the base layers, and 8) how well they performed in terms of warmth, utility, and comfort.

Factors Evaluated
Following are the specific factors I will be evaluating the Zyflex Thermals on. I have provided some information in this Initial Report, and will answer the remaining questions in my Field Report and Long Term Report. 

Fabric—Except for stating that the fabric is 59% Polyethylene, 35% Nylon, and 6% Lycra®, Zyflex does not give a detailed fabric description. It has a lot of horizontal stretch, but very little vertical stretch. The fabric is woven in a very fine grid pattern (see photo). It is claimed to be warm, comfortable, highly breathable, and water-resistant.

Construction, Quality, And Fit—The fabric and sewing quality are very good; I could not find any flaws in either the fabric or sewing. The seams are not flat-felled, except the collar. The construction is also very good - the sleeves are not baggy and are Raglan style to provide greater freedom of movement, the neck opening is right-sized, and the body is well-proportioned, amply long, and has a dropped tail.

Both the shirt (size XL) and pants (size L) fit me very well. I normally wear a size large shirt, but I needed a Zyflex XL (according to their size chart) to get the correct fit, which turned out to be correct. The shirt fits slightly relaxed on me. The sleeves are a little short, and (for me) it would be nice if they were an inch (2.5 cm) longer. Articulation is good; when I cross my arms the sleeves don’t move, and I can feel the fabric stretching across my back. However, when I extend my arms above my head the sleeves retract about one inch (2.5 cm) because the fabric has very little vertical stretch.  The pants fit like tights and easily stretch to fit my legs without feeling tight. When I squat or raise my legs the pants stretch with me.

Performance As A Base Layer—How do they feel against my skin? Do they readily wick moisture away from my skin and dry quickly? Do they hold body heat well? If I wear them while hiking, how comfortable are they at different exertion levels? Do they have a broad comfort range? Are they sufficiently warm (or too hot) for cool/cold weather hiking? Are they comfortable over a wide temperature range?

Performance In Combination With Other Performance Clothing—For example, how well do they perform in rainy weather and moderate to high exertion? How comfortable are they to wear with various outside layers in cold weather activities—like late spring in the alpine country? Does other clothing slip over them easily?

Performance In A Sleeping System—Do the Zyflex Thermals provide a lot of warmth for their weight when worn in a light sleeping bag to extend its warmth?

Odor Management—How effectively do they restrain or eliminate odors? Does washing completely remove odors?

Durability—How durable are the Zyflex Thermals? Does the material pill in wear zones? What is its life span likely to be under the conditions I am using them?

Versatility—What is their versatility for different outdoor activities? In my evaluation, I will assess their utility for various uses, including ultralight backpacking.

Acknowledgement
I would like to thank Zyflex and the BackpackGearTest Group for selecting me to participate in this test.

Will Rietveld