Anything returnable can be sent or taken back. When you buy a returnable sweater at the mall, you have the option to take it to the store and get your money back if you decide you don't look good in purple.
A returnable bottle is one that you can take back to the store and trade in for a little money after you've used or consumed its contents. And when booksellers carry returnable magazines, they can send the unsold copies back to the vendor for credit. When things are returnable, you are literally able to return them.