Both versions of the pants look almost exactly the same as Patrick and SpongeBob's regular pants, except they inflate into a bigger size, as the name implies.
Role in series
The pants seem to be activated by a pull-switch that triggers its wearer to have the pants lift them aloft, only to flip upside-down because of the weighted pressure, as demonstrated by Patrick. The first version of the pants had the ability to irreparably burst off the wearer, upon their request.
"The Sponge Who Could Fly"
The pants make a more prominent appearance when SpongeBob places a hair dryer in his pants, causing them to inflate and help him fly in the sky like a jellyfish, increasing his chances of living with them until he is asked by many townspeople to do favors for them. The pants are later shot down and burst by Cannonball Jenkins.