You put it in the microwave with a little water, no problem. However, if you overload it, the seal gets damaged. So far, I have put two thick 180 ml bottles of Dr. Brown's together with their pacifiers + some other pacifiers without any problem. I also put the accessories from the breast pump. I don't know if a 160 ml bottle would fit. It is practical and fast, but the costs add up over time, even though each bag has 20 uses. Be careful, immediately after sterilization, the oven burns with steam/water.