Moet ik de ruimte tussen de profielen volledig opvullen?

That depends on the type of filling material:

• Glass wool or rock wool (mats): Fill to the thickness of the mat. If your drying floor grid is 6 cm and you're using 4 cm mats, then 4 cm of filling is perfectly fine.
• EPS beads or cork granules (loosely sprinkled): It's best to fill the space completely. This maximizes insulation and dampening, and it's easy to do because you simply sprinkle it in.
• Load-bearing fillers (e.g., aerated concrete granules): Always fill completely to the top. This will provide the slab above with support throughout and prevent sagging or voids.