"Definfitely looks interesting - bear in mind that some users find, say, eVent fabric, while highly breathable, can feel cold when stationary precisely because it is so vapour permeable, so the idea makes a lot of sense."
I thought eVENT was found to be a little chully because it was AIR permeable, not VAPOUR permeable. Afaik, c_change is just a hydrophilic membrane, with a twist that really isn't that important or effective according to tests from the US Army, and so it isn't air permeable.
I think it was, CP. The subject came up in a thread last year I think... but I can't find it (no surprise). The first commercial applications were in motorbike clothing.
Unfortunately, as I recall, the science as set out in the Schoeller marketing site pdf was a bit dubious. So it was hard to tell what the coatings were REALLY doing.
They talk about effects in the Near Infrared (reflecting back some of the Sun's power that is not visible to the human eye) but then go on to say that this affects the rate at which the garment loses heat too (which would have to be in the Thermal Infrared - wavelengths typically about ten times as great as NIR). From what I understand, almost all fabrics behave roughly as black-body emitters in the TIR range...
This is similar to what desired in IRR camouflage. It seems strange to think that you improve your camouflage by making yourself more reflective to Infrared, but the purpose is to mimic the natural behaviour of plant leaves which are reflective in IR (known as Red Edge in remote sensing jargon).
So essentially, you are making yourself behave more like a plant - taking on dark colours in the visible spectrum and reflecting infrared. Good for camouflage and good for staying cool in direct sunlight.
the marketing info for c-change is really confusing. As Tom says it's hydrophilic, and so there is nothing to open up, it's not microporous like eVent. The actual molecules involved in the process of moving vapour may speed up or slow down according to the temp that they set the membrane at. Essentially it's a bit like some kind of memory material. At the temp that they set the membrane at it becomes stiffer when it goes below it, and the process slows causing less vapour to escape. Above the set temp the membrane becomes more flexible, and the molecules speed up, moving vapour quicker. Saw a naff demo with a business card made from the membrane which was solid at room temp and below. If you dip it in hand hot water it became floppy.....I wasn't impressed!
the marketing info for c-change is really confusing. As Tom says it's hydrophilic, and so there is nothing to open up, it's not microporous like eVent. The actual molecules involved in the process of moving vapour may speed up or slow down according to the temp that they set the membrane at. Essentially it's a bit like some kind of memory material. At the temp that they set the membrane at it becomes stiffer when it goes below it, and the process slows causing less vapour to escape. Above the set temp the membrane becomes more flexible, and the molecules speed up, moving vapour quicker. Saw a naff demo with a business card made from the membrane which was solid at room temp and below. If you dip it in hand hot water it became floppy.....I wasn't impressed!
C_change is indeed marketed as a sort of shape memory polymer with special properties. But hte fact is that it is certainly not the first material that is marketed that way. A product like Toray Dermizax, which can also be found under different names in gear (membrain, drytech, cutan, ...) is marketed in the same way. They are presented as a material which retains heat when cold and inactive and which breathes more and more once above a certain temperature. Research doen by the US Army a few years ago showed that these polymers are actually nothing special and are not different than other hydrophilic membranes. There is one graph which showes that at lower temperatures breathability is reduced and a t higer temperatures breathability rising steeply. This is supposed to be the proof for the shape memory effect. But if you compare that graph to the vapour pressure curve, which is temperature dependent, it shows that both graphs are practically identical. In other words, the membrane itself doesn't show any special reactive properties based on temperature; it's al about the normal law of physics.
This is interesting, though from what I understand from what people are writing its more to do with marketing than something you would notice in the field in real use. I remember Marmot having sometime like this around 10 years ago ,it just disappeared after a while,I'll have a look at my old catalogues Smamitman
