We try not to use the word "rare" a lot, but this set seems fairly rare in aggregate. First, we have two sizes of the turquoise blue snowflake pattern space saver casserole dishes which seem a bit harder to find than other shapes/types. But the real rarity, we think, are the aluminum lids! We've never seen them and we really think they are cool! The lids fit in to the Pyrex easily and are much lighter than the glass lids -- and they are obviously not going to chip! Plus, they make these casseroles very easy to stack -- either for display or in your fridge!