This is a handy device for warm weather wilderness camping where you don’t have a cooler or access to ice. You can keep fish fillets or other perishable food items cool by placing them in a plastic bag, wrapping that with a wet cloth, and setting in a cool, shaded spot. I like to set them down in the shade behind a rock, moving away leaves to get right down to the cool, damp earth. If you remember your 9th grade IPS class, you know that it takes calories of heat to change a liquid into a gas. It’s called the refrigeration effect. That is what happens here as the moisture in your towel dries off. The calories of heat are drawn out of whatever the liquid is in contact with - here being your package of food items. You can keep those items around 20 degrees cooler than the air temp, depending on the humidity. This also works well in your pack, as long as the compartment they are in can breath. NOTE: Always use caution with perishable foods. This method gives only marginal protection in warm or hot conditions.