I bought these to replace the plastic containers we had been using for a while.  Because they are glass, they don't stain or leave lingering odors.  The glass container portion can be washed anywhere in the dishwasher, but I wash the lids on the top rack.  So far (4 months later), I have noticed no warping or discoloration in my lids, even with numerous times in the microwave.  These seal TIGHT, but just know that the first couple of times I used them, they took some muscle to close.  Now that they are easier to close, they still kept their tight seal.  The glass is thick (like a pyrex dish), so this makes them heavier than plastic containers, but it is not a negative (in my opinion).  I bought this set and a set of 18, and my mother-in-law purchased a set for herself after using mine a few times.