The Brush Guard! ($5.50 per pack) They help to expand the life of your cosmetic brushes by preserving its shape and allowing upside down dry time (!) after washing.
Caring for your makeup brushes the right way can save you hundreds of dollars in the long run. The most important thing to know is how to wash them. Use baby shampoo, antibacterial dish soap, or makeup brush cleanser to thoroughly cleanse each bristle until water runs clear. Never leave your brushes to dry standing upright. This can cause water to drip back into the ferrule (look at the diagram below), loosening the glue that holds the hairs together. The result? Your $50 powder brush starts balding. Until I discovered these money savers via Michelle Phan, I laid my brushes flat to dry.
If you can't purchase brush guards right away, you can do wonders with rubber bands! :)