许多人都以是否看得出原材料是什么而确定用 be made of 还是 be made from，其实这种说法并不科学的。最好说：表“物理变化”用 be made of；表“化学变化”用 be made from。

be made of之后通常接“物质材料”类的不可数名词，名词前常不用冠词；be made from之后也接原料，但并不限于“物质材料”类的不可数名词，有时可接可数名词，名词前也常不用冠词，多指加工制造。如：

1. be made of表“物理变化”

The chair is made of wood. 这椅子是木头做的。

Everything there is made of bamboo. 那里的什么都是竹子做的。

Is it made of cotton, silk or wool? 这是棉织品、丝织品，还是毛织品？

They are made of steel. 它们是钢做的。

2. be made from表“化学变化”

Nylon is made from air, coal and water. 尼龙是有空气、煤和水加工制成。

These wines are all made from grapes. 这几种酒都是用葡萄酿造的。

Aluminum is made from bauxite. 铝是从铝土矿中提炼出的。

They're all made from soya beans. 它们都是豆制品。

3. 既表“物理变化”也表“化学变化”的用 be made of 或 be made from 均可。如：

Steamed buns are made of / from flour. 馒头是用面粉做的。