Imagine a planet with a thin atmosphere so big that it's almost considered a gas giant and with a super-earth sized core that is about as dense as cotton candy. That planet would belong to a rare new category of planets called the super puffs! Super puffs or cotton ball planets usually weigh as much as several earths but are 10 times the size of earth in volume. Recently two of these planets were discovered orbiting the star Kepler 51 and they both have a density of about 1/10 that of Saturn's - the least dense planet in our solar system.
Super puffs begin their lives on the outskirts of their solar system probably as ice giants like Uranus or Neptune. Then over time these planets would migrate closer to their star where their thick gases and icy cores started to liquefy and evaporate away. Leaving behind a spongy poofy ball.
But before you decide to visit one of these planets keep in mind they tend to hang out close to the star well past the habitable zone. So unless you wanna get fried you're probably better off renting a bounce house instead.