SpongeBob is a sea sponge, like his parents, but he is drawn to resemble a kitchen sponge. It is said that this because Hillenburg found this design to be more amusing. Although in several episodes he is shown to have a spine, he is extremely flexible and can bend in all directions. He can also absorb large amounts of water due to his porous body.
SpongeBob was based on Hillenburg's first sponge kid, Bob the Sponge, who was the main star of the comic The Intertidal Zone. Bob the Sponge looked round, wears sunglasses,and looked extremely different from SpongeBob. Hillenburg shows the true birth of SpongeBob in an audio commentary special feature in Disc 3 in the SpongeBob SquarePants The Complete 1st Season Box Set. Also, the Intertidal Zone was starred with Rocky the Shrimp. Hillenburg reveals the creation of SpongeBob.