Self-deflating air mattress.
This may be obvious to most of you. Maybe you’ve noticed occasions where you fill your air mattress in the afternoon or evening then climb in your sleeping bag only to find it needs another several puffs of air. Or worse, you awaken at midnight with your butt touching bedrock, and you need to reinflate your mattress. Why?

When you fill your air mattress initially, you are inflating it with 98.6 degree air. But after the sun sets and temperatures cool, the air in your mattress cools and contracts. The contracting air can be enough to turn a comfortable mattress into an under-inflated mattress.