GEAR » Stoic VaporShell jacket WPB claims unbelievable -- BackpackingLight.com Forums *** ***. --> Give a gift subscription to a friend who has a pack that's too heavy. Give Now --> Skip to content Help --> Cart Log in Welcome to Backpacking Light! Subscribe Subscribe Home Articles Store Education Courses Publications --> Community Forums Recent Posts Reader Reviews Recent Reader Reviews Trip Reports Most Commented Articles --> School Course Catalog Compare All Courses Course Calendar / Enroll Now Our Philosophy Frequently Asked Questions Course Curricula Photos & Video Our Partners --> Forum Index » GEAR » Stoic VaporShell jacket WPB claims unbelievable --> Display Avatars Sort By: Date (Chronological) Date (Reverse Chronological) J C (Joomy) - M Re: Re: Re: Re: inverse relationship of waterproofness and breathability on 05/27/2011 00:05:54 MDT Aaron, my point is not that there is or should be an inverse relationship between waterproofness *ratings* and breathability *ratings* , it is that in a microporous material there should be (and is) an inverse relationship between *actual* waterproofness, which is amply demonstrated by the standard hydrostatic head test and the *actual* breathability, the best test of which is, I believe, the DMPC. The standard test for MVTR, the inverted cup test, is basically worthless and thus any MVTR data gleaned from it is, I believe, meaningless in the context of this debate.Another reason WPB materials may not display the expected relationship between waterproofness and breathability is because most of these materials (with the notable exceptions of Vaporshell, eVent and NeoShell) use some sort of monolithic, (air impermeable)coating to protect their ePTFE membranes from contaminants. The original Gore-Tex membrane was super breathable and waterproof but was susceptible to damage from the oils in skin. To fix this they somewhat sneakily added another monolithic oleophobic coating to their ePTFE membrane, rendering it oil-proof but also severely reducing its breathability by removing the mechanism of water vapor transfer by convection. Nowadays Gore-Tex and most other WBP fabrics "breathe" through diffusion, not convection. That is, the air impermeable PU layer must absorb the water vapor rather than allowing it to pass directly through it. The reason eVent breathes better than Gore-Tex is exactly because they managed to protect their ePFTE membrane without resorting to a monolithic oleophobic coating: their method allows the ePFTE pores to remain open and thus allows water vapor transmission via convection, or "direct venting" as eVent calls it.In a fabric that uses a monolithic structure, the relationship between waterproofness and breathability may not apply because the primary process which *limits* the breathability of such a fabric breathes is not directly related to how it repels water. Water is prevented from entering the fabric by the outer ePTFE membrane, but water vapor transmission is limited by the diffusive capacity of the PU layer. Only *after* the water has diffused through the PU player does the ePFTE membrane come into play, and usually (read: always) the diffusive permeability of the PU layer is far less than the convective permeability of the ePTFE membrane. The PU player is the "bottleneck" for breathability in fabrics which use it.In fabrics which do not use a monolithic layer, and which therefore have open pores that allow "direct venting", such as eVent, NeoShell, PowerShield Pro and I assume Vaporshell, the expected inverse relationship between waterproofness and breathability characteristic of *microporous membranes* should be evident. Indeed it is: eVent is more waterproof and less breathable than NeoShell or PowerShield Pro and PowerShield Pro is less waterproof but more breathable than the others. This brings us back to my original question of how Vaporshell is able to supposedly outperform NeoShell in terms of breathability and eVent in terms of waterproofness. I just do not see how it's possible and suspect that it merely performs well in the "inverted cup" tests and would not perform nearly as well in the DMPC or in the real world. You must login to post. New Visitors: Create a new account Username: Password: Remember my login info. MEMBERSHIP IS REQUIRED TO POST: You must be a Forum, Annual or Lifetime Member to post messages in the backpackinglight.com forums. SUBSCRIBE NOW » Community @ BPL: View My Profile Change My Profile Community Gear Lists Forums: Forum Index Search Forums Recent Posts Recent Threads New Posts Since Last Visit Reader Reviews: Review Index Search Reviews Last 50 Reviews ABOUT| CONTACT| TERMS| LOCAL RSS Feed COPYRIGHT ©2003-2012 BEARTOOTH MOUNTAIN PRESS LLC U.S. Library of Congress Serial Registrations: BackpackingLight.com (electronic, ISSN 1537-0364) & Backpacking Light Magazine (print, ISSN 1550-4417) BACKPACKING LIGHT® and the FEATHER/MOUNTAIN icon are registered trademarks of the Beartooth Media Group, Inc. 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