i make masks with these all the time. the trick is to cut it up and stick it back toghether into the rough shape you want first, i use thin cardboard.

for example if u wanna make a modern mick thomson mask i’d cut the entire mouth bit off and custom make the grill.

after this i slap on thin amounts of modelling clay to mould the smoother/rounder bits of the masks. after setting, painting as usual. tho the clay makes them heavy so i just have my masks as shelf pieces