Just an interesting observation:
tore apart both a 87U black and 87U white today.
notice that the plastic is different for the two casings
ABS (Acrylonitrile butadiene styrene) for black
PS (polystyrene) for white
on wikie's page for ABS, there is a claim that ABS is stronger than PS:
"The nitrile groups from neighboring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene."