The author (5’7″, 160 pounds) in MontBell’s U.L. Alpine Down Hugger #5.
I reviewed two MontBell U.L. Alpine Down Hugger sleeping bags, #3 and #5, for inclusion in an upcoming article on lightweight backpacking gear for kids. I also used these adult sized bags myself and present my impressions here. These two bags are identical in design and construction, differing only in their weight and temperature rating; a direct reflection of down content and baffle height. The Alpine Down Hugger #3 is rated to 32F and weighs 21.5 ounces. MontBell’s #5 Alpine Down Hugger is rated to 42.8F and weighs 17.3 ounces (BPL measured weights).
MontBell’s U.L. Alpine Down Hugger sleeping bags are hooded mummy-style bags with full-length zippers. These bags are a trim fit. There is little extra girth, and the lengths are kept trim. At 5’7″ and 160 pounds, I found the size regular bags acceptable bordering on an “athletic cut.” There wasn’t room for additional insulation layers within the bag beyond a lightweight base layer or perhaps a fleece sweater. I normally use a homemade adjustable girth top bag and like the ability to add layers to adjust to variable temperatures. With MontBell’s bags, I had to ensure I had enough bag for the conditions without relying on additional clothing layers to stretch the rating. (MontBell offers another line of bags with a more generous cut in their Super Stretch series.)
Not a typical feature among similarly classed bags, MontBell added full-length zippers to their UL Alpine Down Hugger line. The YKK zippers use double sliders to allow venting from the foot up or head down. A single full-length draft tube mirrors the zipper and was very effective at preventing cold air from entering along through the zipper. Although the ventilation options are nice, I would prefer reducing the full-length zipper to a half-length and adding the weight back in extra down insulation. The hood adjusts with a Velcro closure tab and draw cord and was more than adequate to cover the face down to my mouth.
Backpacking Light staff have consistently applauded MontBell’s propriety fabrics and DWR treatments. These bags use MontBell’s 15-denier Ballistic Airlight nylon with DWR treatment throughout. Ballistic nylons are manufactured by heating and stretching the nylon fibers, a process that strengthens the fibers much like tensiling does for steel. Again this material has performed flawlessly, holding up to the ruff-housing antics of my two daughters as they hopped around like inch worms in our pyramid shelter. The fabric breaths well enough (perhaps not as much as some), holds up to abuse, and keeps the down inside.
MontBell fills these bags with 725 fill-power goose down, using vertical box baffle construction. The Alpine #3 has 9.5 ounces of down, and the Alpine #5 has 6.3 ounces. These numbers are a bit lower than the amount of down found in similarly rated bags. This is partially due to the Alpine Down Huggers’ trim fit (allowing MontBell to maintain similar loft with less down) and partially by a few features unique to these bags (discussed below). For comparison, I measure 2 inches of single layer loft on the #3, and 1.5 inches on the #5. Keep in mind, if the trim fit is too trim for you, the effective loft may be reduced as your body compresses, or pushes, the down against the bag’s outer fabric.
MontBell’s U.L Alpine series has two features that set it apart from most lightweight sleeping bags. First, the inner baffle seams, inside the bag, are lined with elastic. The elastic pulls the sleeping bag lining against your body to reduce drafts and convection air currents within the bag. Each baffle traps heat every 5.5 inches throughout the length of the bag. The elastic is only on the inside of the baffles, not on the outside where it would compress the down.
The other innovation is a sealable foot section. The girth around the last baffle is adjustable via a draw cord fed through the last baffle seam. The bottom of the bag can be sealed with your feet inside, trapping heat and mimicking a pair of booties. For those who are too short for one of the two standard length bags, the foot section can be stuffed inside the bag and the draw cord drawn to effectively shorten the bag’s length by 7 inches. Also, the entire sleeping bag stuffs into this foot section, again using the draw cord to cinch tight to reduce the need for a stuff sack.