Tossing tennis balls into the dryer is a popular laundry hack used to fluff bulky items like down comforters, sleeping bags, and puffy jackets. The bouncing balls break up clumps in the filling, improve air circulation, and help your laundry dry faster.How to Use Tennis Balls SafelyUse New, Clean Balls: Only use brand-new or perfectly clean tennis balls so you don't transfer old dirt, dust, or court grime onto your freshly washed laundry.Protect the Fabrics: To prevent bright neon dyes from transferring or loose rubber from scuffing your clothes, place the tennis balls inside an old white cotton sock or a zippered mesh laundry bag.Adjust the Heat: Set your dryer to low or medium heat. High heat can cause the rubber core of a tennis ball to warp or smell strongly of rubber