I have discovered that there is a lack of shavings in the wall at one place in the house, probably they forgot to refill when a closet was built underneath. Anyway, this should probably work to have in the wall: http://www.granngarden.se/product/kuttersp-n--
I could also consider pouring in Ecowool, but I don't know where I can buy a bag? Doesn't feel like something you just swing by the hardware store and pick up a bag when needed. I need so little, maybe somewhere around 1 m2. It's just about filling in from open spaces in the attic.