因为定语从句所修饰的先行词The box 是【成品】,所以用into which引导定语从句

The box 【into which such material is made是定语从句】 is very light and lasts long
这种材料做成的箱子既轻也很耐用.
正常语序：
The box 【which such material is made into是定语从句】 is very light and lasts long

注意这个短语：
be made into (被制成）+成品

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