They’re great for bike packing and if you’re not trying to share a space with someone else/dog. Better than hammocks in my experience and obviously less weight than a tent.
I had an outdoor research alpine bivy that was really nice (goretex) but stolen out of my vehicle - didn’t want to buy another so just kind of tried to mimic that.
The bottom section is duck canvas and the top section just ripstop nylon. They’re basically just a baggy sleeping bag with no insulation and can close however - zipper, cinch string etc
I purchased some waterproof marine fabric today for other projects but that’d probably be good for a bivy/tents. It’s pretty cheap per yard (compared to goretex) and is more waterproof than any of the materials I mentioned above
The bottom section is duck canvas and the top section just ripstop nylon. They’re basically just a baggy sleeping bag with no insulation and can close however - zipper, cinch string etc