How does an Evac Dry Bag / Compression Dry Bag work? Does the Evac fabric prevent air being drawn back in?

Both Evac Dry Bags and Evac Compression Dry Sacks feature a waterproof yet air-permeable Evac fabric base.

• The laminate keeps water out, but air can move freely through it in both directions.
• The fabric does not act as a one-way valve – if you pack down gear like a sleeping bag or puffy jacket, it will naturally expand again as air is drawn back in.
  
  

Using an Evac Dry Bag

1. Pack your compressible item inside the dry bag.
2. Roll and clip the closure securely.
3. Sit or press down on the bag to squeeze out excess air.
4. Once compressed, pack it tightly into your backpack before it can draw air back in – this helps you make the most of your available pack space.
   
   

Using an Evac Compression Dry Bag

The Evac Compression Dry Bag works the same way, but includes side compression straps. Cinching these straps forces air out through the base and keeps the bag compressed. The added straps mean the Compression Dry Bag weighs slightly more than the standard Evac Dry Bag.

Misconception about “breathability”

Laminates like Evac are sometimes described by end users as breathable, but this can be misleading.  While the fabric can allow moisture vapor to pass through while remaining waterproof, this only happens when the inside of the bag is warmer than the outside – for example, in a waterproof-breathable jacket where your body heat pushes moisture outward.

In a dry bag, however, wet or damp gear does not generate heat, so it will not dry inside the bag. The contents will remain damp until removed and air-dried.