Straw was used as insulator as well. Both in footwear and on cabin floors.
Wattle&daub is Stone Age building method (wood strips latticed and plastered/daubed with “wet stuff” and straw). I’m not familiar of its use in pre-historic Finland, but as people migrated from elsewhere, they must’ve been familiar with the building method.
Straw has been made in to decorations: little goats, cows, horses, and stars (with a hair and fine thread through the straw as connector).
Now, *straw is not hay*. Straws nutritional value is near non-existent and only about goats will eat straw. IF cereal plant were to be used as hay, it would need to be harvested for that purpose before the plant produces seeds/grain. Other plants than cereal are grown as hay for animal fodder, mainly timothy and meadow fescue in Finland.