During the Cold War, the U.S. Air Force issued sleeping bags in “spam cans”—steel cans opened with a metal key. Unintentionally silly by today’s standards, it was part of a serious effort to keep crashed or shot-down airmen alive in cold regions until they were rescued.

YouTube vlogger Taras Kul picked up a M1949 sleeping bag on eBay. The M1949, also known as “Sleeping Bag, Mountain, M1949” is well known in collector circles. Introduced in 1949, the M1949 is what we would today call a “mummy bag.” The bag features a cotton shell with down filler and is meant for mountain or Arctic conditions.

This M1949, however, is different: It’s vacuum-packed in a can like Spam. The external markings on Kul's model indicate the bag was part of a U.S. Air Force contract. The contract number is difficult to run down, but it appears the sleeping bag was part of a contract for 1950s-era F-84F Thunderstreak jet fighters. That makes sense since the bag, sealed in a can, is clearly meant to be used only in emergencies.

Why would the U.S. military pack sleeping bags in metal cans? Goose down is compressible, but it’s also really difficult to get all the moisture out of a down bag if it gets wet (unlike modern nylon shells). If an emergency sleeping bag gets wet in storage you might not notice for years, and by the time you really, really need it you could be left with a mildewy mess. Thus the impenetrable metal can.

U.S. air crews that suddenly find themselves on the ground, whether by enemy action or show-stopping malfunction, have other pressing problems than whether or not their sleeping bag smells and feels like a wet dog. They’ll be much too busy evading enemy patrols or finding their way back to civilization to marvel at the ingeniousness of packing a sleeping bag in a giant sardine tin.