This fabric accordion expands at the knees, which gave me—a sleeper with restless-legs syndrome—a welcome night of unrestricted tossing and turning. The elastic keeps the Exceloft synthetic insulation close to the body for efficient warmth, though some cold sleepers found the rating a tad optimistic. 32°F, 2.7 lbs; www.montbell.com
Bonus: A drawstring closes off the last foot baffle, so shorter people can micromanage fit.
Bummer: Extra fabric and elastic add weight.