In reply to Si dH:
Might depend on how long will it stay in the cupboard...
I am not exactly sure about the chemistry of the actual membrane, but I think it is a polyurethane hydrophilic non-porous one? PU is somewhat susceptible to hydrolysis and degradation even in long term storage, even if it might it might be the more environmentally sound option unlike some fluorocarbons. One of my old SympaTex jacket membrane basically peeled off flaking after a decade of not even using it, just like some boots insoles disintegrating. Of course, there are many formulations now and the chemistry might have gotten much better, but you might be better using it or selling it than just storing it for a decade while it might degrade itself. Probably wouldn't be an issue unless you have it in the cupboard for a really long time, though.