Printed on the box of a Kenda inner tube:
You don’t say! 
Phil
Regular Butyl tubes are pretty airtight, but I know that some of the ultralightweight latex ones need pumping up after every ride 
Comment from someone else… “Good thing too, you don’t want any of that pesky air getting inside it!”
Phil
… or outside. Have you ever smelled the air that comes out of an inner tube? Shew!
Yes! Especially if it’s a tube from a crappy old water-logged wheel.
Andrew