Weight: 2 lb.
Estimated Value (Sane Cost Guide): 500 gp
DMG Value: 101 gp - 500 gp
While wearing this cap underwater, you can speak its command word as an action to create a bubble of air around your head. It allows you to breath normally underwater. This bubble stays with you until you speak the command word again, the cap is removed, or you are no longer underwater.
Source: DMG p157