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!

Angelo,

I use a 0.8oz cuben floor on my bivy with no groundsheet. This material is hard to find, so I would recommend the 1.0oz cuben with no groundsheet.

If you use the 0.74oz, you need to use a groundsheet, which brings the weight up higher than if you had just gone with the 1.0oz...

So, should I skip sil nylon in favor of 1.0 cuben?

That is what I would recommend, yes.

If you use silnylon, get the Shield from thru-hiker

I put on bivy floor and it doesn't leak. Richard tested HH and it is much better than other silnylon. Bivy floor is the most difficult application for waterproofness. It is slippery though so you have to put some gobs of silicone to reduce this.

Other silnylon I've tried does leak.

I don't use a ground sheet with my MLD Superlight Bivy, and it has a .75oz cuben floor . . . it's super strong stuff, and if it gets a few holes in it after a few years I don't really see a problem with that. My old ground sheet is covered in holes and patches!

My vote goes for heavier cuben floor. It will be very durable and can be patched with duct tape if it does get punctured. It's also not slippery like silnylon, which can be a good and bad thing. Oh, and I'm not the one footing the bill for it.

I've found that silnylon floor makes for a bivy that packs up a little more compactly though,(compared to a heavier cuben) if that matters to you.

Im also looking at floor options for a bivy, would 1.43 be overkill?

After everyone's helpful comments and some research I went with m50 top and 1.0 oz cuben floor. Can't wait! This will help me attain a 1lb shelter weight.