overlap porous absorber panels

[giuseppe]

Hi to everyone
I have a doubt, to overlap two 5 cm (2 ") panels has the same effect as a single 10 cm (4") panel? Knauf says no, density varies (?), Why?
thnx

[DanDan]

Of course it cannot be precisely the same, but two 2" will be very very similar to a 4"
DD

[giuseppe]

Also in my mind, but Knauf say no (without explanation..)