I was wanting to get away from plastics and use glass to reheat leftovers. I had no idea that there were vented lids that made that operation even better. What a great idea. These work great and I even cook using them in the micro. I cut up potatoes, add a little water, butter and seasoning, pop the lid on and vent, and I have wonderful potatoes in 8 minutes. Can't say enough good things about this product.