A lightly-insulated sleeping bag with an extra-roomy cut that’s used to boost your bag’s temperature rating by 15-20 degrees F. It can also serve on its own as a lightweight summer bag.
The same stuff used for jackets is found in some ultralight warm-weather sleepers.
More durable than the short-staple synthetic fills, these synthetics have long, continuous-filament fibers that make them more durable, but also heavier and bulkier. Polarguard 3D is the best, and most expensive, of these fills.
The latest, greatest version of Polarguard 3D, using a slightly different polymer design, a higher-denier fiber, a bigger void inside the fiber, and thinner walls. What’s it all mean? You get a bag that’s 10 percent warmer and slightly lighter, with better loft and durability.
This synthetic insulation will perform similarly to others, but is heavier and bulkier than newer versions, which is why it typically is found in less expensive bags.