Use in rain is challenging
This bivy is waterproof. However there are a couple things to keep in mind:
1) If you expect ANY rain, be sure to understand that without modification this will not keep you dry.
2) If you expect to be able to sleep with the hood down, be prepared to be damp from condensation in the morning.
I've used this for 60 days in Maine but ended up carrying a lightweight, very small tarp in addition. I set up the tarp and made sure the head of my bivy was underneath. Then, when it rained I could have the hood open, which eliminated condensation and sheltered me 100% from the rain. It also gave me a nice dry place to change, store gear, etc.
overall it's great for a bivy!