![]() However, to me, the critical question will be whether even with “pumping” can the comfort range of the “moderate” permeability windshirt be significantly extended beyond what is provided by a very low permeability windshirt.” You said in part, “I can easily incorporate both internal and external air movement into this test to try to gauge the importance of pumping or low level breezes on moisture management and will take a look at this. In this case, the radiant barrier is in direct contact with another material, so the heat transfer mechanism will be conduction. ![]() Radiant transfer occurs through the air or a vacuum. Not a simple problem to solve, at least not for me.Ĭoncerning your point about insulating layers: If you have a low emissivity coating in contact with other clothing layers, it would do generally nothing. This means that if the otherwise thermally camouflaged soldier walks past a heat source, he can be seen by the enemy who is using his thermal night vision equipment. If you apply such a coating to a fabric, how will it impact breathability? Also, the low emissivity coating will be reflective of adjacent heat. Low emissivity materials are often metallic. If it gets dirty, the emissity will rise. If it gets wet, the emissivity will rise. It has to be difficult to maintain the emissivity of the exterior coating. However, this coating could lead to overheating, in principle, or it could lead to increased comfort in really cold temperatures. If you can successfully reduce emissivity, the exterior garment face temperature will rise, so convective loss will increase. I did a write up of the Columbia solution here: …/evaluation-of-omni-heat-performance/ If so, I will measure emissivity and quantify the impact on thermal resistance. If you can suggest any obtainable garments that I can examine, I would appreciate it. None of the claimed “low emissivity” commercial solutions that I have examined have contributed much in terms of thermal performance. I presume you are referring to an exterior low emissivity coating. I would very much like to examine any LWIR blocking technologies. However, to me, the critical question will be whether even with “pumping” can the comfort range of the “moderate” permeability windshirt be significantly extended beyond what is provided by a very low permeability windshirt. I can easily incorporate both internal and external air movement into this test to try to gauge the importance of pumping or low level breezes on moisture management and will take a look at this. I have voraciously consumed your work for years and appreciate all you have done. Previously it was outlawed for this market. Most news worthy to me is that Patagonia is now apparently using it on commercial garments or the fabric finish of the Patagonia Air has lower emissivity than nylon or polyester. Secondarily it will increase the insulation value as you observed. This coating is primarily intended to make soldiers outer clothing much less visible to IR night vision weapons. Military rainwear and windshirts routinely haveLWIR block coatings applied. I have measured windshirt LWIR transmission through various fabrics. Any WPB membrane and your windshirts will read similarly using your existing MVTR tester but dramatically different with it modified to add air This emulates the pumping motion caused by your body movement. You can modify your custom MVTR tester to add air to the water and clearly see this difference yourself. For active use, these moderately porous fabrics will exhibit an average of around a 300% increase in the MVTR values you indicate. I agree with most of what you wrote there is only one exception: MVTR tests, such as the ASTM E96, or your custom test, give an indication of MVTR for static use only.
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