I am in currently deciding on a bivy. I want to use it year round, so it must handle 4 season weather, and big enough to engulf my neoair and winter bag. My top material will be m90 or m50 with a net window over my face. But the real toss-up is floor material. I am leaning toward cuben, but might go with sil nylon. A couple of custom bivy makers offered .74oz cuben. But to protect the cuben it is recommended to use a groundsheet. It is my understanding that it is ideal to use a plastic groundsheet with lightweight sil nylon because of its lower hydrostatic head (but will also help with damage).
Going by weight alone, if I bring a groundsheet for both bivies, cuben wins.
But if I go with sil nylon and leave the groundsheet home and does it level the playing field or will cuben still be the lighter option?
Longevity, at this point I think I will be fine with either material. I am careful with my gear.
Also, should I consider going with a heavier weight cuben? Will the weight penalty be worth it?
Thank you so much for your help!