be made of silk还是be made from silk

be made of

用...造成(用于原材料显而易见的场合)

be made from

由...所做成的(用于原材料不易看出的场合)

eg. The bridge is made of steel.

这座桥是用钢材造的。

试比较：Steel is made from iron.

钢是由铁炼成的。

silk看得见原材料，所以这里用be made of silk 。