I'm working on redesigning my old trek 4 season tent, and want to build a new, lighter inner for it. What material should I use for the bathtub floor? I'd like to make it light, but don't want to sacrifice too much durability, since the floor does need to hold up to some abrasion (even with a ground cloth). Any input would be appreciated.

What material are you working with currently. 70d coated ripstop is only 2.2oz per yard at 60 inches width. I plan on building some bivys soon with this stuff. I really thought long and hard about some other fabrics but I had to get honest with myself about how hard my wife and I are on gear and how wet it tends to be round here.
At one point I was going to go with some 1.35 oz stuff but them I realized I would just have to carry an extra bit of tyvek to keep it up which does not really save us any weight at all.

The 70d urethane coated stuff is less slippery, the silicone
coated 30d lighter.

If you are using a footprint anyway, I would go with the
30d.

I think the 70 denier "2.2oz per yard at 60 inches width" data may be a bit misleading. It implies 1.32 ounces per square yard.

From what I've seen, 70 denier uncoated nylon is about 1.8 to 1.9 ounces per square yard. Urethane coatings add 3/4 to 1 ounce per square yard; silicone coatings add 0.25 to 0.4 ounces per square yard.

I have a 20 year old tent with urethane coated 70 denier ripstop floor. I've only patched a few places where I did stupid things. Personally I quit using ground sheets on any backpack tents back when I made my first MYOG 25 years ago. I'd rather patch or replace the floor once in a while than always carry a second floor. I don't usually camp on muddy ground though.

Consider using 1.1 basis silnylon and painting an extra coat of thinned silicone caulk on it. That will make it less slippery and more water repellant.

Edited by jimqpublic on 02/18/2009 10:33:10 MST.

First off, do you plan to remove and replace the entire floor? If so, you might be happier using the same general fabric weight as the canopy - making allowance for the coating on the floor. It may just be an aesthetic thing, but generally, a tent feels better to me if the floor fabric is the same or slightly heavier than the canopy fabric. Seattle Fabrics has 1.9 oz silnylon which may be worth considering for reasons discussed below.

Patching the existing floor with silnylon is a good idea. It's a lot easier than constructing a new floor and as James says, a good coating of silicone will make it less slippery.

If you decide to replace the complete floor, carefully remove all the stitching and use the old floor as a pattern. Make careful notes and drawings of how it is put together. In particular, put the coated side on the inside if using PU nylon or 1.9 oz silnylon (which is one-sided like PU nylon).

Be advised that 1.1 oz. silnylon is much less abrasion resistant than PU nylon of the same weight.

The advantage of silnylon is that it won't degenerate and flake or peel off like PU. With care, a silnylon floor will last as long as the rest of the tent.

Depending on the use you put the tent to and its original design, you may need to use nylon thread. Polyester thread does not stretch, but the rest of the (nylon) tent will. When the nylon stretches too much - under wind load, for example - it will break the polyester thread. Use the longest stitch length on your machine. It will probably still be shorter than the original, but that's ok. Some 4-season tents have 3 rows of stitching on the floor/canopy seam. It's tedious to do, but make sure the seam is wide enough to duplicate the original spacing between stitch rows. It's a structural thing.

Thanks everyone for all the great advice! I think I've decided to replace the floor. The sides of the tent are very light material, and I think I can save myself about 300 grams if I replace the floor with lighter fabric. I think I'm going to order some 1.9oz silnylon at seattle fabrics. The total weight of the new floor will be around 400 grams. I'm also gonna replace the way-to-beefy corner rings with something lighter.

Edited by samuraiPrecision on 02/19/2009 00:57:10 MST.

I think you will like the 1.9 oz Silnylon as floor material. I made a Bug Bivy with 1.9 oz Sil from Seattle Fabrics as the "floor" and it has worked out well.

Edited by DBthal on 02/21/2009 19:03:35 MST.

FYI, have purchased the 1.9 oz silnylon from both Seattle Fabrics and Stephenson's, and both weigh around 2.5 oz per sq. yd. So I assume the 1.9 oz. figure refers to the weight before the coating is applied. Used the latter as just the bottom (not sidewall extensions) for a tent (as protection against the claws of my shelties), and found it added too much weight. Bought some 1.1 oz sylnylon with a heavier sil coating for a total of 1.7 oz, a couple years ago from oware and intend to use this fabric for future floors, as it has a slightly heavier coating and is not so slippery. There were some silcoated tarps available at EMS a few years ago which were also lighter than the 1.9 oz (before coating)and were represented as a "codura" product. This material would also be a good compromise if I could find it anywhere.
Realize this is not much help to anyone looking for floor fabric now, but wanted you to know that there is some good stuff out there if one hunts.
Sam Farrington, Chocorua NH