Importance of board density in heat & sound insulation?

[Yrrol]

How important is it that the board material has a high density when you want to have, for example, warm and quiet walls?

 

[yxet]

a lot of "air" in the board provides an insulating effect/porous board is a very effective one, I think it dampens sound a bit too.

 

[Yrrol]

Anyone else daring to speculate?

If you have dual disks, can you add up both of their densities, or is it the one with the highest value that counts?

 

[anaitis]

High sound insulation is achieved through high density and simultaneously low stiffness (E-modulus).
Of commonly occurring sheet materials, only gypsum provides any sound insulation worth mentioning.

 

[FredrikR]

Double plasterboard, absorbs a lot.