I have changed more than 8 for the two thermoses we have (4 in each) and that's because the whole thermos often falls down from the kids, it generally takes a lot of hits and the first thing that "pays the price" is this lid. It breaks the internal gray tooth it has. This tooth presses the straw when the lid goes down and clicks in place, to prevent water leakage. It has happened that this breaks, the side round parts that hold the plastic semicircle above the clear dome, and in general, I have seen all possible damages. I give 1 star less only because it should be made of harder plastic in some areas. Overall, the lid is good but there is no way you won't change it and this will definitely be due to a break that has occurred from a fall. Also, the kids often bite and cut the internal silicone straw, another reason for replacement. Fortunately, it has a low price and you don't think about it. I, with the twins, have gotten tired of buying them in pairs (1 for replacement and 1 for spare) but what can we do, that's how it is with kids. I think the thermos is the best of all we have tried which are definitely more than 5 in total!