Thermochromic filament. Note: it regains its original gray color very slowly - 10 hours. Model at 100% was too small.
measured coffee cup dimensions:
84mm top diameter
61mm bottom diameter
at 100%. the inner diameter of the sleeve was 67mm. Doing the algebra, I need a multiplier in x and y of 122%, but leave the Z at 100%.
I reprinted this at 110% and 120% - 120% seemed best when first printed, but it seemed to stretch a bit when actually used with hot coffee. The higher temperature seemed to make the PLA more plastic. So, although 110% was initially too small, after one or two uses, it stretched to the best fit.
For the 120% I only scaled it up in x and Y, leaving the Z at 100%.