In 1917 the zipper was developed and, of course, these made for a terrific seal for the rectangular sleeping bags allowing an individuals body warmth to remain trapped longer consequently keeping them warmer on those cold winter season evenings. Basically the term resting bag essentially suggests a safety bag for someone to rest in.
The other sacrifice is the size or thickness of the bag. A mummy sleeping bag essentially will certainly be much smaller sized for bring around which is why it is a preference for many backpackers/hikers. The rectangular resting bag isn't as small yet because it's not common to be lugging it, apart from somewhere in a vehicle while getting to your intended location, the bulkiness of the bag is not as large a problem.
Goose Down Resting Bag: There's nothing with a greater weight to warmth proportion when compared with down. A Goose Down resting bag is extremely light-weight. Down is only for people most diligent in maintaining their sleeping bag completely dry. Hood: as detailed previously with the Mummy Sleeping Bag, a hood having a drawstring could assist keep temperature.