Quote Originally Posted by soulsurvivor View Post
got it.... still. no fabric is "waterproof" that i know of. not sil-nylon or cuben. for that matter it has to be that the weave of the fabric is tighter or it is treated in more coats / with better silicon.. guys that have used 100% silicon are getting good results right? so it must just be that scotchy is inferior. bummer cuz the price cant be beat. unless you go for that tyvek ugly tarp... not lookin so ugly these days lol
I'm not sure why you think "no" fabrics are waterproof. A high quality silnylon, good PU coated materials, cuban, etc., are for all intents and purposes, waterproof.

The DIY silnylon discussed in this thread uses a silicone sealant (caulk) disolved in mineral spirits to soak the fabric. After the mineral spirits evaporate and the silicone cures, the result is a fabric with the space between threads filled with silicone.

A silicone spray/scotchguard type product coats the surfaces of the threads but does not fill in the voids. It raises the surface tension (or something similar) of the fabric and causes water to bead up. Water "pounding" on the fabric (rain) can still be forced between the threads causing leaks. A bag made of this type material and pressurized will leak as well.

While my details may or may not be a little off, I believe the general ideas to be correct.