Learn Finnish: Onko tuo laatikko metallinen vai puinen?

They are formed by adding the suffix -inen to a noun stem to describe what something is made of. The noun metalli (metal) becomes metallinen (made of metal), and puu (wood) becomes puinen (wooden).

Why does this sentence use vai for "or" instead of tai?

In Finnish, vai is specifically used in mutually exclusive questions where you expect the listener to choose one of the options provided (it has to be one or the other). tai is used in regular statements, or in questions where the answer could simply be yes or no.

If I wanted to say "in a wooden box", how would puinen change?

Adjectives must match the case of their noun, and words ending in -nen change that ending to -se- before adding case suffixes. Since "in a box" is laatikossa, "in a wooden box" becomes puisessa laatikossa. In our sentence, they are in the basic nominative form.

Could I use a compound word like metallilaatikko (metal box) instead?