There’s no perfect insulation. Whether you’re looking for a jacket or a sleeping bag, you’ve likely encountered the trade-offs between down and synthetics. Down is extremely warm for its weight and compresses to take up very little space in a pack. But the feathers clump and are useless when wet, and they tend to spill out if the shell material tears, making field repairs tricky. Synthetic fills, which are made in sheets rather than individual fibers, retain warmth when wet and stay in place when the outer fabric tears. But they’re heavier than down and don’t pack down nearly as well.
Nemo may have come up with a solution. The company’s new Azura sleeping bag ($200 and up) features a new synthetic-insulation construction called FeatherCore, which, according to Nemo, is as light and compressible as 650-fill-power down. (For reference, 650 fill falls in the middle of the down spectrum with regard to packability: top-level products have 800-fill down, which is as warm as 650 but weighs less and packs smaller, while low-end products have 500-fill down, which is far heavier for the same warmth.) FeatherCore consists of regular PrimaLoft Silver insulation that’s manipulated to reduce weight and bulk. Nemo says the technology is proprietary and did not go into specifics on exactly how it made the existing synthetic fill so much lighter.
Having spent too many mornings wrangling stubborn synthetic bags into their stuffsacks, I was dubious. But after getting my hands on the 20-degree Azura, I’m convinced that Nemo is onto something. The bag stuffs down into a package a little bigger than a loaf of sandwich bread and weighs 2.6 pounds. Most other 20-degree synthetic bags weigh three pounds or more. (The Azura comes in 20- and 35-degrees versions, and in regular and long lengths. The men’s version, called the Kyan, comes in the same specs.)
Weight aside, the Azura features a 20-denier ripstop outer, nylon taffeta on the inside for a soft next-to-skin feeling, and Nemo’s trademark zippered vents along the top, called gills. I haven’t had the chance to use the Azura out in the wild yet. But the prospect of a sleeping bag that offers the versatility of synthetic insulation without completely sacrificing on weight and bulk seems like a win in my book.
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Correction: We incorrectly described FeatherCore as a new insulation. In fact, it is an existing Primaloft fill that's been manipulated in a new way. Outside regrets the error.