My personal experience is that it is superlight and pretty waterproof. I have spent a few nights in light rain in it and been dry. I would recommend putting the seamsealer that comes with it. If you want something totally waterproof I could recommend the http://www.backcountry.com/store/BLD0267/Black-Diamond-Hooped-Bivy-Sack.html?RSC_ID=WR_BLD0267 It is fully waterproof. The Winter bivy is superlight and compact but isn't designed for week long rainy backpacking trips. I can understand any apprehension on your part. It's like being on a rope for the first time. Trust your gear. It will perform just fine.