Swap your plastic electric toothbrush heads out for bamboo! These toothbrush heads are compatible with Phillips Sonicare 9-Series and have medium/soft bio-based bristles. Each toothbrush head should last the recommended three months with daily use.Made of: Sustainably grown bamboo with bristles made from castor oil and infused with charcoal. These bristles are totally biodegradable. The insert on the bottom is made from cornstarch PLA and is required for the metal to fit and vibrate effectively.