Choosing A Compression Sack

From backpacking and bikepacking to kayak adventures—compression sacks are always handy when space is at a premium.

These space-saving miracles can compress bulky items like sleeping bags and down jackets to almost a third of their size—making more room in your pack for precious peanut butter and chocolate.

(Exactly how much reduction in volume you can expect will depend on the materials of the product you are trying to compress).

To help you get the right compression sack for your adventures, we’ve answered some of your most common questions around this handy space-saver.

WHAT SIZE COMPRESSION SACK DO I NEED FOR MY SLEEPING BAG?

Because sleeping bags vary in their packed volume—depending on whether you have a down bag or synthetic bag and what shell and liner fabrics they use—it’s not possible to simply equate a bag temperature rating with a compression sack size. Instead, you’ll need to determine your sleeping bag’s volume and equate that to liters.

HOW DO I DETERMINE THE VOLUME OF MY SLEEPING BAG?

If you’ve bought a Sea to Summit sleeping bag, you can look up the volume of the bag on our product pages. If you’re determining the volume of another bag, follow the process below:

• Put your bag in a cardboard box (one which is larger than the bag)
• Measure the length and width of the box in inches
• Press the sleeping bag down firmly until the upper surface is roughly level in the box
• Measure the average depth that the bag occupies in inches
• Now multiply length x width x depth = volume in cubic inches
• Divide the total by 61 = volume in liters
• If you live in a country which uses the metric system, measure in centimeters and divide the total by 1000 to calculate the volume in liters

WHAT KIND OF COMPRESSION SACK SHOULD I CHOOSE?

WATERPROOF + DURABLE: EVENT® COMPRESSION DRY SACK

Choose it if: you need compression and waterproof protection, and weight is not of critical importance.

This is our original award-winning waterproof compression dry sack—the first on the market without a purge valve, and still the standard by which all compression dry sacks are judged. Instead of a purge valve, we used air-permeable eVent® fabric on the base—air can be rolled out, but water can’t get in. Made from durable 70D polyurethane coated Nylon and designed with four straps for even compression.

WATERPROOF + LIGHTWEIGHT: ULTRA-SIL™ EVENT® COMPRESSION DRY SACK

Choose it if: you need compression and waterproof protection, and weight is critical

The Ultra-Sil eVent Compression Dry Sack is the lightweight version of our crowd-favorite eVent Nylon Compression Sack. Made with 30D Ultra-Sil fabric, it’s 40% lighter than our original design but still retains our revolutionary eVent fabric base—eliminating the need for purge valves.

One word of caution: the Ultra-Sil fabric is not designed for external use (i.e. on the outside of a backpack or bikepacking rig). If the use you have in mind requires external mounting, choose the eVent Nylon Compression Sack.

LIGHTWEIGHT + NOT WATERPROOF: ULTRA-SIL™ COMPRESSION SACK

Choose it if: you need a lightweight compression sack that doesn’t need to be waterproof.

Thanks to our 30D diamond ripstop Ultra-Sil fabric, the Ultra-Sil Compression Sack compresses your gear down without adding noticeable weight. It’s designed to compress evenly and a slippery finish on the fabric makes it easy to shove into the tight spaces of your pack.

COMPRESSION SACKS AREN’T FOR LONG-TERM STORAGE

Compression sacks are great on the trails but make sure not to store your sleeping bags or down jackets in them for too long. The compression can damage the delicate clusters of down or synthetic fill.

DURABLE + NOT WATERPROOF: NYLON COMPRESSION SACK

Choose it if: you need compression, water-resistance and durability

Our 70D Nylon Compression Sack offers an excellent strength-to-weight ratio, making it our most durable water-resistant compression sack. Four extra-long straps compress bulky items evenly, and a Nylon webbing pull-handle makes it easy to remove from your bag.

PACKING SLEEPING BAGS AND INSULATED JACKETS: THE EVAC DRY SACK

Choose it if: you need waterproof protection but don’t need maximum compression

The eVac dry sack compresses a little differently to our other bags. Pack your soft items in the sack, roll and click the roll-top closure closed, then sit on the bag to squeeze out air through the eVent fabric base. It doesn’t need straps and a lid to compress; instead, simply roll the roll-top closure down tighter until you’ve achieved a reasonable degree of compression. You’ll need to pack the bag into your backpack and pack other gear on top to prevent it drawing air back into the sack.

Compression sacks make hauling gear around so much easier—and, fortunately, there’s one for almost every kind of adventure. If you need the dry storage without the compression, reach for a dry sack or dry bag instead. Too easy.