Compressibility
The North Face Furnace 20 improves nighttime warmth with the addition of a layer of synethic insulation—TNF’s Heatseeker Eco—through the bottom of the bag. This synthetic layer didn’t compress when I laid on it like down would, meaning it provided good insulation underneath me throughout the night. But what won’t compress at night won’t compress during the day either, and this layer negated the compressibility and weight savings of using down in the rest of the bag. The Furnace stuffs down to a bulky 9-inch by 17-inch bundle. Not huge, but not exactly a compact package. 

Warmth
The Furnace 20 earned its name for the most part. The bag’s down fill and synthetic underlayment kept nighttime chills at bay. But the bag’s hood sabotaged the bag’s warmth rating. I couldn’t get the hood to comfortably cinch around my face—when it did get snug, it pinched and puckered along my temples and under my chin. When I got it comfortable, it let in drafts of cold air all night long. However, our testers who don’t typically cinch their hoods dubbed this bag a true furnace. 

Features
The water-resistance down insulation was much appreciated by myself and my team during testing in the Olympic Rainforest as we discovered one of the tents we were also testing leaked like a sieve during a typical Olympic downpour. I also appreciated the architecture of the footbox—it was roomy without being a cold-air vault. 

Overall Comfort
The ill-fitting hood marked the one significant complaint I found with the overall fit and comfort of the TNF Furnace. The footbox was perfectly designed and the shoulders and hip sections offered plenty of room for me to move through my various normal progression of sleeping positions—side to back, back to stomach, stomach to side, repeat. 

Durability
During testing in eastern Washington’s highland steppes, I slept out under the stars amidst highly abrasive basalt rock formations. Even though I slipped off my sleeping pad more than once, and a couple times caught the bag on a sagebrush branch, the Furnace didn’t get so much as a snag in its shell. This is a stout bag that will withstand years of use and abuse.

Value
Because the Furnace 20 is warm, comfortable, and durable, it is worth the investment. The fact that is sells for well under two bills easily makes up for its weight and bulk.