Synthetic vs. Down: Which is Best for Your Thru-Hike?


Most insulation works by capturing air inside material clusters. A jacket or sleeping bag that more effectively captures and retains heat generated from the body has better insulation.

fibers under miscroscope

Fleece Fibers (Synthetic)

Fleece is made from polyester fibers which are synthetic. Fleece is a comfortable but tough durable fiber that allows moisture to evaporate. The image shows the thick fleece fiber up close. Fleece is made by weaving these thick fibers and the brushing them into a fluffy thick fabric.

Fleece fibers are shown at about 25x magnification. One white square is 5 mm by 5mm (about 0.2 inches by 0.2 inches).

Large Fleece Jacket Weight: 586 grams (20.7 ounces)

Fleece Blanket (70 x 54 inches) Weight: 1559 grams (55 ounces)


  • Affordable and durable


  • Heavy, poor insulation, and doesn’t compact well
fibers under microscope

Thin Synthetic Fibers

The image shows the thin fibers extracted from a synthetic puffy jacket. The thin synthetic fibers take up a lot of volume and fill up a lot of space. These thin synthetic fibers provide much more warmth than fleece.

Synthetic fibers from a puffy jacket are shown at about 25x magnification. One white square is 5 mm by 5mm (about 0.2 inches by 0.2 inches).

Large Synthetic Puffy Jacket Weight: 454 grams (16.0 ounces)

15°F Synthetic filled sleeping bag Weight: 1446 grams (51 ounces)


  • Affordable and compact


  • Heavier and less insulation than down
fibers being examined

Down Insulation

The image shows down (800-fill-power) extracted from a down jacket. Down creates thousands of small air pockets that trap warm air. Down is not only a great insulator but also compacts to a very small size.

Down is shown at about 25x magnification. One white square is 5mm by 5mm (about 0.2 inches by 0.2 inches).

Large Down Puffy Jacket Weight: 378 grams (13.3 ounces)

15°F Down Sleeping Bag Weight: 936 grams (33 ounces)


  • Best insulation, easily compacts, and lightweight


  • More expensive and poor insulation when wet


Out of all the insulating materials down still remains the best. Down has a warmth-to-weight ratio about two times that of synthetic insulation. Down is also lighter and compacts better than the synthetic materials. However, down is much more expensive than synthetic insulation.

Most long-distance backpackers and thru-hikers select down as their insulating material. The best insulation for your hike will depend on your personal hiking needs.