Synthetic Insulation: The Long and Short of It

If you've shopped for outdoor gear, you've seen the zillions of labels identifying what type of synthetic insulation is in that coveted sleeping bag or jacket. Primaloft, Polarguard, Thinsulate, Climashield... the list goes on and on. But do you know which of these are short staple and which are continuous filament? And why it matters?

Short-staple insulation consists of a huge collection of short synthetic fibers, each usually less than 2 inches long, that interlock with each other to create a layer of insulation. In contrast, continuous filament insulation consists of a single, long fiber that weaves around and interlocks with itself.

The fibers in short-staple insulation are often smaller in diameter than those used in continuous filament. This, coupled with the fact that the fibers are able to move more or less independently, makes short-staple insulation more compressible than continuous filament. The fibers are also more tightly packed together, creating more dead air spaces—and thus more warmth for the weight. The short length of the fiber creates a much puffier, down-like feel; most garments stuffed with short-staple insulation will be very soft and flexible, draping closely against your body. Finally, this type of synthetic insulation is the most compressible synthetic insulation available.

The downside? Short-staple insulation has a tendency to move around over time and use, creating lumps and cold spots—especially after months of repeatedly cramming it into a stuff sack. (For this reason, you seldom see short-staple insulation in sleeping bags.) It also tends to lose loft (and thus warmth) faster than its continuous filament brethren. Most versions of Primaloft use short-staple insulation. Thinsulate is another.

Continuous filament insulation is more durable and retains loft longer than short-staple. It also tends not to shift around with use and abuse. This is what you usually find in sleeping bags. Continuous filament is relatively stiff, however, which makes it less desirable for use in jackets and other garments. It does tend to retain more loft and warmth over time than short-staple insulation. Insulations from Polarguard and Climashield usually feature continuous filament technology.

All this raises a bit of a dilemma. When they're new, short-staple insulations are clearly better than continuous filament: lighter, warmer, and more compressible. But fast forward a year of regular outdoor use. Now the continuous filament is warmer for its weight. Hmmm... (Note that neither will be as warm as the day you bought it; all synthetic insulation loses a noticeable amount of loft and warmth with use.)

At least now you're armed with the knowledge to make the decision that's right for you!

Equipped” is an AMC Outdoors blog, written by Matt Heid.

Image courtesy of Primaloft.

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