Temp-Sensing Discoloration helps parents to keep track of milk temp at any time. Purple is Cold(<36 degree C/96.8 degree F), blue is Optimum Feeding Temperature (36-40 degree C/96.8-104 degree F), and white is Hot (>40 degree C/104 degree F). Designed with double sealed side seams & double zipper to protect and freeze breastmilk. When sealing, press your fingertips and make a sound. Presterilized & BPA/BPS free thickened milk bag, safely build your milk bank. Milk import/export separation design ensures that there is no contamination. Simply open the sealing strip when pouring milk, and cut along a cutting line when you need to breastfeeding. It's that easy! Breast milk storage bags can be freezed super flat or upright. This unique feature also allows defrost or freeze milk quickly. Friendly Tips: Capacity is not exceed 6oz. After milk is poured into the bag, it is necessary to release the air. After thawing, heat it to 40 degree C (104 degree F).