The second layer has a clear mission: to retain the heat your body generates. Keep in mind, your jacket doesn't generate heat on its own; instead, it works like a thermos, trapping your body's temperature and preventing it from escaping through radiation, while allowing sweat to escape. When choosing your insulating layer forascend, the debate is always the same: Down or Synthetic?
Goose Down: The Gold Standard
Down offers the best weight-to-warmth ratio on the market. It's incredibly lightweight and compresses so much that it barely takes up any space in your backpack.
- Fill Power:Assess the down quality. A 600 FP jacket is excellent for classic trekking, while 800 FP or more is used for high mountain.
- The weak point:Its vulnerability to moisture. If the down gets wet, it clumps together and completely loses its ability to insulate against the cold.
Synthetic Insulation: Versatility and Durability
Brands with technologies like Primaloft® or Thermoball® developed fibers that mimic down, but with a huge technical advantage against the weather.
- Moisture resistance:If synthetic material gets wet (from rain or your own perspiration), it still retains body heat.
- The weak point:They are garments a bit heavier and bulkier than down when packed away.
Which one to choose for your trip?
If you are going toexploreIn dry areas or areas of extreme cold (like the high Andes Mountains), down is your best ally. If your destination is Patagonia, where the weather is unstable and precipitation is frequent, synthetic insulation will give you much more peace of mind and thermal security.