Not ready to give up your electric toothbrush yet, but hate the waste? Swap to our bamboo electric toothbrush heads! They have medium/soft bristles made from castor bean oil and blended with charcoal. Bamboo is naturally antimicrobial and a fast-growing renewable resource. Includes: Four refill heads in kraft paper boxes. Compatibility: These refill heads fit most "click-on" Philips Sonicare electric toothbrushes including all 9-series models. They will not fit specialty models, screw on models, Oral-B, etc. Recommended: Dentists recommend to change your toothbrush head every 3 months. Bio-Based Bristles: Made from castor oil and infused with charcoal, these bristles are biodegradable. Insert on the bottom is made from cornstarch PLA and is required for the metal to fit and vibrate effectively. The words "Phillips Sonicare and 9-Series" are to express compatibility, not for trademark. This product is not sold by Philips Sonicare.