We are really happy with our Pyrex set. The sizes are just right for a variety of leftover types and stack together nicely (except for the one size with an extra piece, which is somewhat of a straggler in the storage area). The tops are tight and fitted to curve around the edges of the glass, so you have to kind of work them on to seal them. Despite this, they aren't exactly leak proof - the only reason I'm not giving 5-stars. I haven't had any major spills but when I use them to bring leftovers to work it is absolutely necessary to put them in a plastic bag during the commute. We haven't tried heating them yet/using them for hot liquids, but the glass appears thick enough to handle hot soup and they are supposed to be microwave safe. Also, please note that "18 piece" means the 9 containers and 9 lids, not 18 containers (we knew this but thought some people might misinterpret the product name...)