Sandy's air helmet is a helmet worn by Sandy Cheeks so that she can breathe underwater. However, she does not wear it in her treedome, as it is already an air-polluted/water-free location of Bikini Bottom. It first appears in the episode "Tea at the Treedome."
It is an air helmet with a pink flower on the upper-left side.
Role in series
Sandy is required to wear this air helmet when outside of her treedome to make it so that she won't die from a lack of oxygen, as seen in "Pressure" where her lungs deflate after being challenged by the sea creatures to breathe without her helmet and she quickly puts a pickle jar over her head to recover.
However, when in her treedome, she removes the helmet, as well as her astronaut suit and boots, since her house is an air-polluted area of the ocean that doesn't require such equipment.
The first episode where Sandy was seen without wearing her air helmet in the ocean was "Pressure."
There are similar devices worn by sea creatures to enter Sandy's treedome called "Water Helmets."
In "Mimic Madness," SpongeBob is inexplicably able to imitate Sandy while wearing her air helmet without dehydrating from a lack of water. He and Patrick are also able to enter her helmet without dehydrating in "Rodeo Daze."