Descriptions Bumble Bee PP Breastmilk Storage Bottles are made of BPA-free polypropylene (PP), approved by U.S. FDA.  Researches have shown that PP is the BEST & SAFEST plastic for breast milk storage in  retaining breastmilk’s beneficial properties. PP bottle resists scratches, splintering and cracking.  It can sustained heat up to 120°C. Sterilization is not an issue to keep these bottles sanitize and clean. Compatible with major brands breast pumps.  The bottles universal thread size allows the bottles to be screwed directly to most breast pumps & express milk directly into storage bottles. If you are using a wideneck breastpump, you can simply use a bottle adaptor (sold separately) to connect your breastpump and the storage bottle directly.