The thicker the glass, the higher the likelihood of cracking when boiling water is poured in. Since glass is a poor conductor of heat, the inner layer will heat faster than the outer layers, expand sooner, and cause material stress. Stress fractures will initiate at edges or flaws, grow and shatter the glass. In contrast, thin glass will obtain the new high temperature more uniformly more rapidly and experience less stress.

A thick-glass remedy is to use borosilicate glass (e.g., Pyrex, Durnan, Borosil), which has a coefficient of thermal expansion (CTE) = 3.3 10^(-6) K^(-1) which is about a half that of ordinary glass. This glass contains boric oxide, is made at higher temperatures, and is on the low end of ordinary glass densities: 2.4-2.8 g cm^(-3). The thermal conductivity of Pyrex is 50% higher than ordinary glass (1.5 vs. 1.0 W/mK), so the outside of your measuring cup will get hotter faster.