Part of Marmot's ultralight range of sleeping bags, the Hydrogen offers a superb balance of quality, low weight, packability, and performance versus cost. It's comparable to many more expensive products, as it is lighter and more compressible than almost all of its competitors. The Marmot Hydrogen uses 800+ fill power down protected with Marmot's Down Defender to help the down to stay dry longer, loft better when damp and dry more quickly than untreated down. The Pertex Microlight fabric offers a combination of lightweight and good durability plus its DWR coating will offer some water resistance. The fabric feels really soft which allows the down to loft freely and the slightly brushed feel of the Microlight lining fabric is extremely comfortable against your skin.
The temperature comfort limit rating of -5C sounded optimistic for the amount of down in the bag but having used a Hydrogen in Scotland in March it seems to be correct. I was using an insulated Thermarest All Seasons SV mat and wearing lightweight baselayers in the bag in the same way that the comfort rating is. On a frosty night I ended up opening the zip slightly as I was so toasty. If you are a cold sleeper you might need a warmer bag but for me it was perfect on a night with temperatures dipping just below zero. This was helped by the excellent hood design which works brilliantly. I’ve never used a sleeping bag with a hood that works as perfectly as the Marmot. Your head naturally sits in the fitted hood and when it gets cold and you zip the bag right up and close up the hood it totally encases your head leaving only a hole in the exact place where your mouth and nose are. Another feature worthy of a mention is the small extra zip which allows you to roll the top of the bag down. This is perfect for a warmer night to avoid overheating or for a cold evening where you want to be sitting in the bag inside the tent.
I got to test the hydrophobic qualities of the down when part of my sleeping bag got wet due to some condensation (due to a not fully tensioned fly as the ground was very rocky). The bag stayed warm and the following day I laid it out in the sun during a lunch stop and it was totally dry and the down returned to its normal loft by the time we moved on. To steal the words of Mr Remington, having tested the Hydrogen I liked it so much I bought one for myself as I didn't want to give it back. The Marmot Hydrogen is an excellent 3 season bag made even sweeter by the price.