like patagonia black hole duffel Noble Grey 55L Patagonia Black Hole Duffel Guide:

I figured it would be something like push the canopy open, doff your headset, and go over the wing-root to get clear of the airplane

These are especially useful on coolers that lack waterproof zippers, as they allow you to lift and maneuver the bag into a vehicle or onto a boat while keeping it upright to prevent leaks

Icemule's Boss has a similar valve system, though in this case the process involves adding air to boost cooling and buoyancy, then removing it to compress the cooler for storage

The size expands and contracts by 20-40 liters

We also wish, as mentioned above, that the bladder insertion point was a bit larger to make it easier to throw in some water and go

Either way, we think there is a good reason that belt bags are so popular, and theyre both great waist bags