Hi,

I've been playing with the idea of making a bivy once I'm done with my overmits. Something for emergency use only, or inside a snowcave. The materials I wanted to use are silnylon for the bottom and something light and breathable for the top. I haven't settled on a pattern yet, but making a bathtub floor seems reasonable. So seams will need to be sealed. Which brings me to my question; if you make the seam between the breathable material and the silnylon a felled seam, should you fold the silnylon over the breathable fabric, or the other way around? I was thinking sealing the seam would be better when done on the silnylon side.

(other tips and advise are appreciated too)

Thanks!

If you put the flat felled seam on the outside, folded down over the bottom, then it's sort of like a shingle on a house, the water will tend to stay outside.

Or you could have the seam inside and fold it up, similarly the water will tend to flow down, rather than into the seam.

Silnylon floor isn't totally waterproof. If you coat it inside with 1:10 ratio of silicone caulk to mineral spirits then it makes it more waterproof. Several opinions about the exact ratio on a recent MYOG thread.

Thanks! I hadn't thought about having the seam on the outside. That makes a lot of sense.

Arranging the seam like a shingle is very good - required in fact.
Trying to proof the seam is wasted effort: the breathable fabric right next to it will leak.

Cheers