This is very similar to the Marmot Lithium MemBrain which we did an in-depth review of. It is the same bag sans Membrain shell material. It's two ounces lighter and $80 cheaper than the MemBrain. The standard Lithium is better for those who bivy less or if going lightweight is a higher priority. Otherwise, we think two ounces is not much weight to get the awesome waterproof breathable MemBrain shell. Overall, the Lithium is one of the warmest, if not THE warmest bag we tested in our Cold Weather Down Sleeping Bag Review.