The Alternative to DownSynthetic insulation can be found in mid-layers, stand-alone jackets, and parkas. Unlike down fill, synthetic insulation will insulate even when wet. It's also less expensive. The type of insulated jacket you choose depends on use. For hanging out on belay or cruising town in the cold all you need is warmth. If you're skiing, backpacking, or climbing, weight and fit become more important.
A synthetic-insulated jacket with relatively little insulation makes an excellent choice as a versatile mid-layer when you're moving or your primary layer when you're just hanging out by the campfire. Opt for a jacket with more insulation if you're standing around while belaying an ice climb or you know you'll encounter brutally cold weather.
A Guide to Jacket Insulation
Most synthetic-insulated jackets use a lightweight or medium-weight nylon shell with a water-resistant DWR coating. However, a puffy with fully waterproof fabric will be worth its weight in gold if you think you'll encounter wet weather.
Waterproof Technologies & Materials