We're working out what we think - we'll add our view here!
Western Mountaineering says:
The Nanolite Quilts are high performance sleep systems designed for the ultralight fanatic. Compatible with any mummy shaped sleeping pad, they boast high functionality and light weight performance. Current quilt designs suffer from poor closure, leading to excessive heat loss. We've addresses this with the addition of a top collar that drapes around the shoulders of the user, locking in core body heat. The NanoLite's unique but simple bottom closure system boasts full closure from shoulder to foot. This closure system also allows for shoulder and hip girth that fit a wide range of sizes and body types.
The lengths of these bags are unique due to their non hooded design. The regular length is made to fit regular length pads while the long length is designed for long pads. The bags themselves are 5'8" (175cm) for the regular and 6'4" (195cm) for the long. Boasting a 7 denier shell and our 850+ fill down, the Nanolite achieves exceptionally high warmth to weight ratio and packs down to minuscule sizes.