The Invisible Spray is a blue bottle that is pretty small in height. It also has "Invisible Spray" written in red with a yellow background similar to the Exploding Chewing Gum. There is also a "warning" box with a red background at the bottom.
SpongeBob and Patrick used the Invisible Spray to prank the people of Bikini Bottom, by making themselves invisible and pretending to be ghosts. At the end of the episode, Mr. Krabs threw water at SpongeBob and Patrick to make them visible again at the Krusty Krab, where they were revealed to be naked, making everyone there make fun of them.
When Frank was holding the Invisible Spray bottle, the bottom of the bottle had a "Danger" sign on it. However, in every other shot of the Invisible Spray, the "danger" part is missing. This may be because the "danger" part is a separate sticker and was ripped by SpongeBob and Patrick.
The Invisible Spray stains clothes which is the reason why Spongebob and Patrick were revealed to be naked after Mr. Krabs splashed water on them.