Either type may be made with hollow threads. The hollow interior reduces weight, and traps air for insulation. Some synthetics are microfibres with textured surfaces that reduce air circulation and increase warmth. More technical bags are designed for maximum lightness and compressibility, and some loss of thermal effectiveness is expected over time. Relatively bulky, heavy and durable insulations are used for applications where weight is less critical.
Most synthetic fills keep their loft when wet.
For this reason, many will consider synthetics if there is any chance of getting wet. The wide price range virtually assures you of finding a bag warm enough at a price you can afford. Performance when wet All bags will yield poor performance when wet. Bags used on paddling trips are easily protected with a dry bag. All bags should be air dried during the daytime hours.