The Sealing Disc Allow You To Store Or Freeze Your Precious Breast Milk, Without Leaking. Please Keep In Mind That The Sealing Disc Has To Be Used With The Philips Avent Adapter Ring In Order To Prevent Leaking.You Can Write The Date Of Expressing Or Freezing On The Sealing Disc. Easily Organize Your Breast Milk Or Baby Food.Philips Avent Sealing Discs Are Made From Polpropylene (Pp) & Thermoplastic Elastomer (Tpe), Two Bpa Free Materials.Easily Store Your Milk And Food In The Philips Avent Bottle. Close The Bottle With The Sealing Disc.Compatible With Avent Natural And Classic Bottles.