What material for bathtub tent floor

The few possibilities are Tyvek, Nylon, or polyethylene plastic.

Tyvek is fairly waterproof, fairly cheap, and wears OK. Nylon has lots of varieties, but if you have a fully-coated nylon like Sil-nylon, that works. It costs more, but it wears better, and probably weighs slightly more. Plastic comes in all sorts of thicknesses. It is cheap, extremely waterproof, but is easily punctured. Depending on the thickness, it may or may not be the lightest.

The nylon fabrics are probably best if you are going to turn up the edges and corners and sew it. Tyvek can be sewn, but plastic will tear.

For one heavy-duty purpose, I made my bathtub floor out of coated nylon. It's heavy. For a quick/disposable purpose, I made one out of 0.7 mil plastic, but I expect it to last no more than a week or so. Previously, I had made one out of 1 mil plastic, and it lasted much better.

–B.G.–

I would use 1.1oz silnylon which actually weighs about 1.4oz/yrd.

here a link to some tips for sewing silnylon (I hear it can be pretty difficult to work with)

http://www.specialtyoutdoors.com/tips/silnylon.asp

About thirty years ago, I sewed my first bivy sack. It was coated nylon on the bottom, and Goretex on top. Worked good, except that it was about three inches too short. So, I made another one, about seven feet long, two people wide, and with netting at the top. Worked good, except that it was too heavy with those materials of that era. I still use it on occasion. Now, with the lightest sil-nylons, it ought to be a breeze.

–B.G.–

Penny is no fool at this stuff.

She helped me once about six years ago.

One trick that I found about sil-nylon. I've tried cutting it with different tools, and I found the best to be a new single-edge razor blade.

–B.G.–

Unless you have a very taught system, and very tall "walls", a bathtub floor is nul. I discovered this when I made a net-tent with a "bathtub floor" (only 2" "walls") which when pitched looks just like a flat sheet, except at the corners.

As for material, sil-nylon is ubiquitous and functional; it also will soak up a tiny bit of water (and more, if you are in a puddle), where you're lying down, as it not really waterproof like other fabrics, including Cuben (and urethane coated nylon), are. Whatever you use, have a bit of an overhang, and don't camp on dished ground.

is what i used for this myog bug bivy floor
the silnylon goes up 5cm/2 inches i added a cord + lineloc to tighten the pitch.

worked well for me, even camping in puddles of water in Scotland when i didnt find any dry ground during a very very rainy week in may last year

its one year old now and used for about 40 nights and still in very good shape