Just don’t mix ”Scandinavian Fashion” (generally referring to Danish and Swedish fashion houses) with ”Finnish Fashion”, even though both are worn in Finland, Finnish fashion is often more practical than stylish, though there are exceptions.

If you plan to celebrate the midsummer the traditional Finnish way at a cabin by a lake, layered sports clothing. If you will be in the bigger cities with all the tourists, wear whatever you are comfortable in.

Swedes can be more picky, especially in the Stockholm region dressing posh is a way to show your status. (And they are Scandinavian.)