Marmet Alpinist Bivy

Justin,

I am a big bivy/tarp fan. My experience with waterproof/breathable bivys is that they don't breath. And after a few days in sub-freezing/high dew point weather, your sleeping bag is going to get soggy unless you have the time and weather to dry it out daily. And in the high Sierra you can get snow any time of the year. With a waterproof bivy it is critical that you keep your head outside and don't breath into your sleeping system. If you do, you are guaranteed to have a wet bag in the morning.

With a tarp, you don't need a waterproof bivy, just a water resistant one. Take a look at MLD's Soul Bivys, TiGoat, or BMW bivys.

For really cold wet weather I use a REI Mimalist waterproof bivy with a vapor barrier liner inside the bag. With this system I may opt not to use any other shelter. Or I may bring my poncho/tarp or a tarp tent. VBL's aren't for everyone, and most people hate them. But over the years I have learned how to use it successfuly. Because I don't do a lot of these cold trips, I opted for the inexpensive REI. It is a lot lighter than the ancient waterproof bivy I had for years. Because I am a cold sleeper, I use down bags and must take extra precautions to ensure the down stays dry. If I did a lot of these cold wet trips, I would probably look at a synthetic bag or quilt. But I have invested a lot of money into my WM and Marmot down bags, so I don't want to purchase another sleeping option.

For milder weather and a good chance of rain, it is a MLD Soul Bivy Side Zip (water resistant/very breathable) with a poncho/tarp.

For summer trips with a low change of rain, I usually skip the bivy all together and use a poncho/tarp, unless it is an extended trip with no way of prediciting the weather. With a tarp tent, there is always more condensation than a tarp, unless it is pitched fairly high off the ground.

Tyvek or poly sheets are good for keeping the bottom of a bag and pad dry when not using a biy.