I have several of these in two styles. Had to call the company to learn that the lids are very stiff, especially when new. Run the lid under warm/hot water and they'll get enough flexibility to safely attach and remove. They are favorites of mine for leftovers and reheating, but I wish the lids didn't require this extra step. Even after a year I still need to warm them a bit to cover tightly. Once covered, no spills!