Synthetic-filled sleeping bags have long had a couple of well-known advantages over down-filled bags, particularly when it comes to water resistance (since synthetics won't collapse when wet, like untreated down does) and lower cost. The trade-off is usually that synthetic bags are heavier and bulkier than their down counterparts. Mountain Hardwear's UltraLamina synthetic bags challenge this assumption. These bags, which are widely acclaimed as the lightest and most packable synthetic bags on the market, rival their down-filled cousins in weight and stuff size; the UltraLamina 32 weighs 2 pounds (898 g) in size Regular, and packs down to a stuffed size of just 6" x 10" (17 cm x 25 cm).
Many sleeping bags, down and synthetic alike, use quilt-style construction in which the shell is stiched directly to the lining in order to form compartments that keep the insulation in place. While this is a simple and inexpensive way of doing things, it means that there's no insulation along the stitch lines - and that can translate into cold spots for the body underneath them. Mountain Hardwear's Lamina technology welds the shell and lining fabrics directly to the insulation, avoiding those pinch points and ensuring that no part of your body is left uncovered.
The UltraLamina bags also feature a unique zipper configuration. Dual two-way zippers extend about 1/4 of the way down each side of the bag, allowing you to flop the whole top of the bag off of your core for ventilation, or stick your arms out of the sides to grab things while remaining in the bag - handy if you're fumbling around for something in the middle of the night. The only downside - it's not so good for those with hot feet, who might do better with a traditional one-sided full-length zipper.
Feature list from Mountain Hardwear:
- Performance mummy cut is snug, reducing girth, weight, and bulk and maximizing thermal efficiency
- Patent-pending, welded Lamina™ construction construction enhances loft and eliminates cold spots
- Ultralight shell is soft and highly wind resistant
- Thermic Micro™ fill is soft, lofty, compressible, and durable
- Comfort Footbox follows natural foot position for maximum warmth and comfort
- Dual #5 zippers minimize weight and provide ventilation options
- Zippered pocket at shoulder for storage of watch, lip balm, etc.
- Face gasket and tailored hood comfortably block drafts at the hood opening and seal in warmth