A NEW PARADIGM FOR UNDERSTANDING WPB FABRICS
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Woubeir,
Thank you for your feedback. Two of your four points were helpful.
Point 1 – You said, “Rab’s Flashpoint-fabrichas/had a claimed MVTR of 60000 and Toray Dermizax NX up to 50000.” Your info was helpful.
Point 2 -This is the relevant Gore-Tex patent abstract:
The picture Gore used to show the 3 layers of ePTFE initially used in Gore-Tex Pro and later ShakeDry. To me it looked the same as my interpretation of their abstract; with the tight microstructure in the center.
In Gore’s own advertising graphics they sometimes refer to their Pro version”s membrane as being a “Dual Layer ePTFE Membrane”.
In /#post-3521225, I said to Michael in part, “The current ShakeDry material is comprised of two layers of PTFE bonded together. The outer FPTE has relatively big pores (patent says open microstructure) and inner PFTE layer has relatively small pores (patent says tight microstructure)”. I didn’t mention a third PTFE layer because the patent abstract inferred it was an option by saying “may be” positioned on the second PFTE layer.
In post #Â 3521293, you responded in part by saying, “Actually, GTX Pro and Gore Shakedry use 3 layers of ePTFE: the first (most outside layer) has small pores, the second (in the middle) has larger ones and the third (near the skin) has again the small pores and acts as a catch-layer for sweat,”
Your info was helpful.
Point 3 – You said, “you don’t need large pores to be air permeable; you need consistent sized pores”. PTFE has relatively consistent sized pores that can be made “open” microstructures or “tight” microstructures to use Gore’s terminology. I thought that open and large could be used as synonyms.
Point 4 – You said, “Perhaps I’ve read this wrong but it’s not because the RH is 100% where the rain is formed, that the RH is also 100% several 1000 feet below, where we live.”
Where I live, 100 % relative humidity only occurs at ground level during fog (you can clearly see 100% RH). It is not uncommon inland of the ocean to have 100% RH in the clouds and 50-60% RH at ground level before or after a short rain storm.
Woubeir,
Thank you for your challenging suggestion to not discount the 50,000 to 60,000 JIS L 1099-B1 g/m2/24hr MVTR claims for multiple products (ZPacks Ventrice, Kuiu, Bergans, ect). My original guess was wrong, they weren’t all using a MP PU membrane that goes to 0 breathability during hard rain. I discovered that they were all using Torray’s Dermizax NX hydrophilic membrane which, in its present form, has been available since 2010. Hydrophilic membranes only reduce their MVTR ~ 57% after 3 hours of hard rain.
I first calculated the ratio between the eVent MVTR number for the Columbia hard rain test vs its JIS L 1099-B1 test result. A JIS 1099-B1 tests gives approximately 2x the MVTR value as the Columbia hard rain test. I then used that ratio to calculate what the Dermizax NX MVTR value would have been for the Columbia hard rain test. I then reduced this estimated dry value to a wet value using the historical reduction value for hydrophilic membranes during hard rain to contrast it with the Columbia hydrophobic outer technology MVTR which doesn’t appear to decrease appreciably in rain.
it appears that it will meet its MVTR limit at approximately the same sub 7 MET point as the Columbia Outdry EX and EX FW membranes previously reviewed. As a plus, it would breathe better than Columbia alternatives if you used it as wind shirt. As a neutral, its MVTR limit in rain is about the same as the Columbia products tested. As a negative, you would face the big temperature drop from wet out that you wouldn’t with the Columbia products plus the attendant weight increase if stored wet
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