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Reviews > Clothing > Underwear > Zyflex Thermal Shirt and Pants > Roger Caffin > Field Report
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Reviewer Details
| Reviewer: | Roger Caffin |
| Age: | 60 |
| Gender: | M |
| Weight: | 63 kg (139 lb) |
| Height: | 167 cm (66") |
| Email address: | r dot [surname] at acm dot org |
| Home: | Sydney, Australia |
Backpacking Background
I started bushwalking at 14 and took up rock climbing at University with the girl who became my wife and my permanent walking partner. Ski touring and canyoning followed. Winter and summer, we prefer long hard trips by ourselves: about a week in Australia, up to two months in Europe/UK. We prefer fast and light in unfrequented trackless country. We would be out walking and skiing for at least three months a year. We have now moved to lightweight gear, much to our backs' relief. I designed and made much of our lightweight gear myself.
I am also the maintainer of the Australian aus.bushwalking FAQ web site www.bushwalking.org.au/FAQ/.
Product Information
| Manufacturer: | Zyflex | www.Zyflex.com/ |
| Year of manufacture: | assumed 2006 | |
| Country of manufacture: | Romania, using American fabric | |
| Size: | Medium | |
| Material: | 59% Polyethylene, 35% Nylon, 6% Lycra | |
| Care: | Cold wash, do not tumble dry | |
| Colour: | Grey (I think) | |
| Model: | Thermal Shirt | Thermal Pants |
| Listed weight: | 7 oz (198 g) | 6.6 oz (187 g) |
| Actual weight: | 8.0 oz (228 g) | 6.2 oz (175 g) |
| MSRP: | US$19 | US$19 |
Product Claims
More complete details about the product are given in my Initial Report. Briefly, these are thermal underwear, but the fabric is a bit different from my previous experiences of thermal underwear. The effect of the inclusion of some elastic Spandex in with the microfibres is very noticable.
I was supplied with both Medium and Small versions, and have been wearing the Medium version. The Medium Pants seemed tight at the start but the Medium Top seemed very loose.
Relevant Personal Background
I have spent 27 years as a research scientist working in the field of Textile Physics. This has given me some experience with fabric construction and fabric physics. In addition, I have been making walking gear and walking clothing for the last 20+ years, and have considerable practical experience in design and sewing. I mention this here as I am making several critical judgements below.
Field Impressions
Home wear
The clothing has been worn at home, under light outer clothing, and at night time inside my sleeping bag in the field in the Blue Mountains during winter.
The 'feel' of the fabric itself continues to puzzle me. It contains Spandex, which is elastic, and this seems to give it a feeling which is part rubbery and part light canvas. It rustles like light canvas as well. I am left wondering whether the weave is tighter than it should be for a couple of reasons, detailed below.
After wearing the Medium Pants for a day I noticed marks from the seam down my skin, above and below my knees. This suggested that the legs were rather tight, and I became concerned as to whether they were too tight and might restrict the blood flow a bit. This caused me to be rather cautious about where I tested them in the field. The top photo shows the Pants fitting tightly around my legs.
I also noticed, from wearing the Pants around at home, that the tight legs seemed to be forever working their way down my legs. Granted I have solid leg muscles, and obviously my legs do taper from hip to ankle, but the way the Pants kept creeping downwards was not satisfactory. I was forever hitching them back up around my waist.
The elastic around the waist has been very good: it has stayed flat the whole time and not rolled up like many other waist bands I have met. It is neither too loose nor too tight by itself, although it is not tight enough to stop the downward migration when I am walking around. I don't think anything comfortable could prevent that.
The Medium Top is a loose fit on me, which is strange when the Medium Pants are so tight. The body is a bit loose around me, but the shoulder region is really loose. The former might simply be an accomodation for fatter people than me (I'm 63 kg or 139 lb), but the loose shoulder region is definitely the result of the design. The region around the arm pits is huge, and drafty. The neck design seems to be rather open at the back and tight at the front, and this allows the shoulder region to let these drafts in; a polo neck would have blocked most of them. The looseness may also be seen to the right and also in the first photo, where the Top almost gives me a bust!
I also tried wearing the Small top for a day to see if the fit might be any better. This was not successful: it was not a good fit and it kept riding up my body. The shoulders were the wrong size as well. I do not think I fit the Small size of these thermals.
Field wear
I packaged the Zyflex thermals up for a trip, and found that they are quite bulky. The long bag has the Medium Zyflex thermals, while the shorter bag has a set of fairly heavy 'other-brand' thermals, packed at about the same 'pressure'. The two blue lines are 100 mm (4") apart. For all of the difference in volume, the Zyflex set weighs only a little more at 14.2 oz (403 g), while the other brand set weighs about 13 oz (370 g). It seems the Zyflex fabric is rather solid, and this is consistent with the appearance of the fabric under magnification. The fibres seem very closely packed, tied together by the black threads. This close packing is part of the fundamental fabric design, and it concerns me as it may be displacing trapped air, which is the real insulating medium.
I tried the full set out on a weekend trip up over the Ironpot Mountains (780 m or 2560'), down across the Cox River (200 m or 656'), and up the Cronje Mountains (942 m or 3090') to camp on Whipcrack Spur. The night time temperature dropped to about 3.5 C or 38 F (I carry a miniature data logger on these trips to record temperature and humidity)). I tried wearing the full set inside my ultralight sleeping bag for the night. The sleeping bag has a Pertex Microlight shell with 300 g (10.6 oz) of 800 loft down, and I have previously used it with my locally-made thermals to -5 C (23 F), which is way sub-freezing. In the middle of the night I found I had cold legs, but this was really strange as my core (upper body) was warm enough and my feet were warm. The latter was really wierd: cold legs normally mean cold feet but my feet were warm. I lay there and thought about this for a while, and decided that having warm feet meant that enough warm blood was circulating down my legs to my feet and back up. I was generating enough heat, and it was getting to my feet. So why wasn't the warm blood keeping my legs warm?
Then I remembered how tight the pants are around my legs, and my concerns about whether they might restrict the blood flow. Blood to my feet goes down an artery deep within my leg to my feet and then returns in a major vein up my leg to my core. What keeps the surface of my leg warm is the flow of warm blood through the capilliaries in the skin around my leg, and that flow is effectively separate from the flow through my feet. Perhaps the flow through the capilliaries in the skin around my legs was being strangled? So I pushed the Zyflex Pants off my legs and down to my ankles. I could tell my legs were warming up in about 5 minutes. I removed the thermal Pants completely and replaced them with my ultra-lightweight silk pyjama trousers. (Why silk pyjamas? To keep my sleeping bag clean. Pyjamas allow me more room to wiggle than a silk liner bag.) I spent the rest of the night quite warm. I can confirm that the night did not suddenly warm up at that stage as I have checked the graph from the temperature data logger I had with me: it stayed cold right through to dawn. For 'thermal pants' to make my legs cold rather than warm seems to me to be a serious hazard and fault.
The Top was not too tight, but I have to say I noticed the drafts around the upper part of my body during the night. I do not experience such drafts with my locally-made thermals, which weigh slightly less than the Zyflex Top. I put my silk pyjama top on over the Zyflex Top, and this seemed to improve things a bit for the rest of the night.
Maintenance
The top and pants have been washed a number of times after being worn around home and on the Cronje Mt trip. They shown no sign of any change in size from the washing. They show no sign of any surface wear either. The fabric seems very robust. The cuffs on the arms and legs don't seem to have changed from being worn or being washed either.
However, while the Zyflex thermals have gone through the washing machine with no problems, drying them is another matter. A pair of our locally-made synthetic thermals, some poly-cotton knit underpants, some polycotton knit skivvies (long-sleeved T-shirts) and the Zyflex thermals were washed together in the morning and hung out to dry together in the sun. The local thermals dried quickly - they always do. The poly-cotton underwear items were dry a little while later. But the Zyflex thermals still felt wet when I squeezed them in the evening, and they had to be brought inside and dried in front of the fire using radiant heat. This is not what I want from thermal underwear: I want it to be fast-drying in case it gets wet in the field!
Why does the Zyflex fabric take so long to dry? My tentative explanation is based on the tightly bundled microfibres making up the weave mentioned earlier. When the microfibres are packed very tightly they can form a sealed bundle. This will trap some air very well (although rather inefficiently in my opinion), but this will also trap any water that has got inside the threads, in between the fibres. The water can stay there for a long time as it simply does not have enough access to the outside atmosphere to evaporate.
Sewing
The construction of the seams has given me some concern. Particular points of concern are as follows:
Inspecting the sewing on all four items has left me with the impression that the Small Pants have been sewn well, while the other three items (Small Top, Medium Pants and Top) have been sewn with much less skill. Obviously this is a subjective judgement, but having done a lot of sewing myself I stand by it.
Water repellency
Included in the testimonials on the Zyflex web site was the following: "There are many companies selling performance clothing that will keep you warm but, very few have anything that keeps you warm and repels water!" I commented in my Initial Report that "the 'repels water' bit is certainly an interesting claim relative to most other thermals, which seem to wick water up at a great rate." I realise that this is a 'testimonial', but it seems to me that the company would not feature it on their web site if they did not endorse it.
I tested this by holding the fabric under a gently running tap. At a low gentle flow the water just ran off without wetting the fabric. This was most impressive. Under a stronger flow the surface of the fabric did start to pick up a small amount of water, but not a lot. Out of curiosity, I tried doing this to some other lightweight thermals I have - ones made with microfibres and displaying a very smooth surface. The same thing happened! As both fabrics have a smooth finish and use microfibres, I am willing to believe that the microfibres can, under some circumstances, have enough surface tension to repel water, or maybe they press so tightly together so as to not let the water into the threads. This is strange as my lens-cleaning cloth claims that its extraordinary cleaning power and absorbancy comes from ... microfibres. However, other (nice warm) thermals with a fluffy surface do get wet quite easily. I have not pursued this further.
Planned Future Testing
I will continue wearing the Zyflex thermal top at home under sheltered conditions. However, in view of my experience on Cronje Mts, I am not willing to use either the Top or the Pants in the field during the winter season. My wife and I push the lightweight gear concept fairly hard and walk fairly hard in isolated places in poor weather, and I cannot justify the risk.
My wife has tried wearing the Small size set which was supplied, but did not find them satisfactory after the first few hours. Her comment was they just were not comfortable enough. They have not had any further wear.
Things I said I would be monitoring in the Zyflex Top and Pants include:
