This warmer lunch box can keep the food warm 3-4 hours but varies depending on your local station, the weather and temperature, the exact time cannot reach this keep the heating time. It outer shell is made of plastic PP material, and the inner tank non-magnetic stainless steel, durable and BPA-free, which is safe, eco-friendly and reusable bento box. It can be heated in the microwave. Remove the lid of the bento box and heat it in the microwave for 3 minutes to enjoy delicious food straight away. It is perfect for daily use by children and adults. Perfect to be used in the office, work, school, kindergarten, picnic as a snack box or wherever you want to go, helps to plan a well-balanced diet.