Lansinoh Breastmilk Storage Bags are durable and leak-proof, with double seals and double seams for strength. Tamper evident and secure tear-away top keeps bags free from contaminants. Lansinoh Breastmilk Storage Bags include a gusseted bottom that allows for expansion when freezing and include a convenient write-on tab so that you can date your breastmilk. Lansinoh Breastmilk Storage Bags are pre-sterilised and BPA and BPS free.