The tenth survival system on the Mountaineers Ten Essentials list is Emergency Shelter.

Everyone who has seriously climbed much has a story about a forced bivouac after being benighted on a cliff or on the descent. When you’re out climbing in the backcountry, stuff happens beyond your control. Heavy thunderstorms move in and strand you up high. A blizzard whips across the great divide and maroons you below the summit.

Or the climbing just takes a lot more time than you had planned. If any of these scenarios takes place, you better have most of the Ten Essentials in your pack, but especially an emergency shelter.

An emergency shelter is essential for survival if you’re caught out in bad weather. If you have plenty of clothes and a good rain parka, the third Essential, you’re going to be well-insulated from wind, rain, and snow. But if you also have a shelter, you’re sure to stay dry and will survive the night. Survival experts say anything you bring for a shelter is better than nothing. Likewise, you need to use your brain and be able to find natural shelter if possible.

The usual shelter that most climbers and hikers carry is a small, lightweight space blanket that easily tucks in the corner of a pack. These were originally developed by NASA in 1964 for use in space. It’s basically a thin plastic sheet coated with a metallic layer which reflects up to 97% of heat. They’re used to keep a person warm and helps avoid hypothermia.

The reality, however, is that they don’t work that good in bad weather conditions, especially in snow. When I’ve used them, I find them unwieldy, difficult to manage, hard to wrap around my body, and precipitation easily leaks around the edges. Still, they’re better than nothing.

A better option is one of the new generation ultralight tarps. Many of these weigh well under a pound, including one from Bozeman Mountain Works that checks in at a mere 5.7 ounces. A tarp is waterproof, easy to set up, and can be configured in various shapes to fit the environment. They’re also compact and easily fit into a pack pocket.

Other options are plastic tube tents, bivy sacks, and even a generic black plastic trash bag with a drawstring. If you’re climbing in winter or in snow above timberline, consider carrying a thin ensolite foam pad to insulate your body from heat-sapping snow. A snow shovel is essential to carry in winter for digging a snow cave. On the opposite end of the weather spectrum, remember to bring a shelter if you’re climbing in hot places. It can provide life-saving shade.