Are Ziploc Bags Microwave Safe?

It's a familiar tale. You get home late from work and you're starving. You go to the fridge and see a portion of last night's tasty lasagna in a Ziploc bag. The option of heating it up in a pot is off the table. It will take too long and just be a mess to clean-up. And then you wonder, "Is it possible to just heat it in the Ziploc bag?" The answer is yes, it is, but with a couple of caveats.

The maker of this simple but ingenious invention states on its website that it is safe to microwave food in Ziploc bags, but only to defrost or reheat an item. Translation: No baking or cooking. However, before you pop that bag of leftover lasagna into your microwave, remember that some types of food fare better than others in the microwave. Ziploc warns that if your food item is filled with lots of sugar or fat, these morsels of deliciousness are going to heat up much quicker. How can that be when microwaves are all about seeking out those water droplets to heat up? 

While your microwave is actively moving water molecules, rapidly bouncing them around and off of each other so they heat, the oil molecules aren't staying still. This is because the glycerol in these fats is absorbing those microwaves and heating them up quicker. So, if you have a cheesy, meaty dish in a Ziploc bag that you are trying to warm-up in a pinch to satisfy those hunger pangs, do so with caution. 

When you are heating something that contains sugar, you also need to be careful because if your kids' science experiments have taught you anything, it is that microwaving sugar can lead to burns and broken dishes. When heated by itself, sugar melts and even burns in a microwave. When it is mixed with other ingredients, the sugar will still absorb those microwaves and get hot really fast. This is why it is also important not to forget to ventilate your bag. Just leave a little slit open at the top. The Ziploc brand maker recommends its bags be opened one inch wide so that the heat and steam can escape as its contents warm up.