Probiotics are living creatures and need to be protected by harsh environments which can damage them such as heat, light and moisture. Natren uses only dark glass bottles with tin lids to protect them from harmful light and moisture. Plastic bottles allow moisture to get into the bottle contributing to a loss of potency of live bacteria. Natren Probiotics are to be stored refrigerated and are shipped in chilly (eski) bins with commercial grade gel ice packs to keep them cool.
Some brands do not require refrigeration if their manufacture guarantees potency at ambient temperature.