I just came across this study:
…..Two commercially available membranes are considered in this thesis: a spunbonded polyolefin manufactured by DuPontâ„¢ with the trade name Tyvek®, and a two layer polypropylene laminate material manufactured by the 3Mâ„¢ Company with the trade name Proporeâ„¢.
The moisture transfer effectiveness of the system depends mostly on the ability of its membrane to transfer water vapour. This effectiveness is investigated by measuring the vapour diffusion resistance of Tyvek® and Propore™ using a dynamic moisture permeation cell. For Tyvek®, the average vapour diffusion resistance is 440 s/m, which corresponds to an expected typical RAEE energy recovery effectiveness of 52%. For Propore™, the average vapour diffusion resistance is 140 s/m, which corresponds to an RAEE effectiveness of 62% in the same exchanger system.
The air permeability is also measured using the DMPC with Tyvek® having a Darcy air flow resistance of 27 nm-1 and Propore™ having a Darcy air flow resistance of 111 nm-1. The lower air flow resistance of Tyvek® is undesirable since air transfer is undesirable in the RAEE system.
The liquid penetration pressure is determined using a modified standard method that resembles the geometry of a membrane in the RAEE exchanger. It is found that the Proporeâ„¢ has a liquid penetration pressure beyond the measurement capabilities of the apparatus (276 kPa); while the Tyvek® membrane has a liquid penetration pressure of 18 kPa which agrees well with published values……
…..The degradation of Tyvek® and Proporeâ„¢ with UVC exposure is also investigated. It is found that both materials deteriorate when exposed to UVC radiation, and that the degradation is primarily a function of the exposure time and not the exposure intensity.
Considering all material properties tested, it is concluded that the Propore™ membrane is a better membrane choice for the RAEE than the Tyvek® membrane.
My take on this: Propore (as in Frogg Toggs) is more waterproof but also more breathable than Tyvek. Am I getting that correct?

