Perlite helps potting mixes drain faster and make the soil lighter overall. It will also store water and release it slowly. Perlite is an important addition to any mix to avoid compaction over time as well. 

Pre-bagged perlite comes in a resealable bag.

If you are shopping in-store you can buy perlite by the scoop (1L per scoop) and take them home in your own reusable container. 

Bring your own container to fill and save 10% on all soil bar products.