I am making a simple bug bivy for summer use I have some ripstop nylon I could coat would that be enough for the floor ? I understand the hh on It is probaly not the best but here in mexico the ground is almost never saturated enough to make that a promblem the floor is more to keep the pad and bag clean and protected from sharp objects

You could just build the entire thing out of 1.25 oz tyvek.
Other than that I would say 1oz silnylon for the bottom.

Whether we are talking about a bug bivvy or a regular bivvy, most people use some fabric that is fairly waterproof for the bottom. That suggests coated ripstop nylon, silnylon, or spinnaker fabric. I used the latter becaused it seemed to be the lightest in weight at the time.

--B.G.--

I have an old GG Spinnaker sheet. It is 24 inches wide and 72 inches long. It weighs a few ounces and works great...in fact, I have had it now for 5 years

Make it out of anything and use Suluk46's 1/8" X 25" X 74 Padded Ground Sheet foam pad as your ground sheet. This is what I often do. I think it weighs 2 oz or so. If you need more cushion, bring another thicker pad.

It might be challenging to construct, but it'd be pretty slick to use the ground sheet as the floor for the bivy. In this case, a Suluk46 pad. I've thought about doing this with an inflatable pad...

I plan on doing exactly that. I've got a good stash of 1.1oz ripstop leftover from my 8x10 tarp project (uncoated) that I intend to use as the floor of the smd meteor bivy, and will coat them both myself. We'll see how big of a mess I can make with the diluted silicone. I imagine I should wear some hobo clothes that I can just toss when I'm done...

I just need to buy the water proof breathable fabric for the top, and some netting and I'm good to go.

BM