Original Pyroflite Microwaveable Bat Warmer Keeps bat flexible as designed by keeping it at the bat manufacturers recommended temperature. Increases confidence resulting in better hitting consistency on the field, especially in cool weather Prevents bat cracking and denting of any composite, aluminum or wood bat Eliminates bat sting and vibration making any new bat feel like it is already broke in An absolute must have for games and batting practice, and will accommodate any size, model, brand of baseball or softball bat This product has a high heat source. It comes with one microwaveable hot pack which lasts 4 to 6 hours. Thebag is made of tuff nylon insulated with heavy dense foam a zipper closure & fence clip