"He feels like a rubber dream."
The Helium Slime is known as the "Balloon Slime" and is only found in Space Station S. L. IME.
Helium Slimes are Aerial Slimes which feels like it's running out of air, so they eat the space air. If they run out of helium, they will turn into Rubber. They only eat Space Air, so you need the "Space Protecter" to keep these slimes alive.
These slimes are hard to catch, as they try to get away when you are being sucked up. You have to go backwards so you can hold your movement, so you would capture the Helium Slime. You can also get the "Harder Vac-Pack" to catch Helium Slimes faster.
Helium Plorts can make Plort Balloons, Plort Helium Gas, etc.. They have many uses!