by Jon MS » Thu 25 Jun, 2020 7:38 pm
About 5 years ago I got a roll of tyvek on the recommend of a friend.
After a couple of years using it I gave up on it and used the rest of the roll when we built our new house a year ago.
I found that tyvek only lasted about 10 nights before it started to leak and it was useless by about 20 nights usage. This means that it was hopeless for waterproofing although it was good for puncture protection. And, in order to be effective, you still have to waterproof inside the tent. If you put tyvek under the tent and there is driving rain, a bit of water gets in under the fly and on top of the sheet which then comes through into the inner (as happens with tent footprints). Also, tyvek is a micro-pore fabric so if you keel on it, you can push water through it which is probably why it leaks after a few uses.
I have found that a much lighter, far more waterproof solution is to buy a lightweight tent knowing the floor is not waterproof and put a painters dropsheet inside the inner. Because it is inside the tent the dropsheet lasts over a year and maybe 75 nights of usage. The dropsheet is totally waterproof, weighs about 100 g (a similar size tyvek sheet weighs about 250 g), is very compact and I cut it large enough so it can go up the sides of the inner about 150 mm so any splash under the fly does not get through. If you get a hole in it (normally when stuffing it into the tent stuff sac), it is easy to patch with a bit of blister tape.
I am not concerned that this system will shorten the life of the tent's floor. If you look at my MSR tent, you can see through the floor but the tent is dry inside (the tent has been used for over 1000 nights over 15 years, but when I say the tent is 15 years old, only the inner fabric is that old with the pole, fly and zips on the inner having been replaced).
A dropsheet is also much cheaper. I find that a about $7 dropsheet from a hardware shop is large enough to make 2 groundsheets for a 1 person tent plus 1 groundsheet for a 2 person tent.