I used to have one vest, now I have two, one down, one synthetic. Synthetic is good if its wet, sort of survival mode. Down warmer for the weight.
Vest is about 1 square yard. There’s an extra inside and outside fabric, about 1 oz/yd2, so two vests weigh an extra 2 ounces.
I have a hybrid bivy/quilt. My current one has the outside fabric M50, but it has rows of stitches for each baffle, so it’s not as weather-proof. I’m making a new one with an extra layer of fabric with the rows of stitches for baffles, the M50 on the outside has only stitches around the perimeter, so it’s more weatherproof. The extra layer of fabric is 1 oz/yd2, 3 yd2, so an extra 3 ounces.
A mouse nibbled on my old one which I fixed with McNett Seam Grip. I am gradually using up its lifetime. I don’t like to make new things that replace perfectly good old things.