The Natural Philosopher wrote:

Ecotherm (and I guess most of the others) do a PIR foam / cork
laminate board for just this purpose. Its 100mm thick and offers good
thermal performance with reasonable sound insulation as well. It looks
like:

http://www.internode.co.uk/loft/images/insulation1.jpg


How can I say it loud enough

THERMAL INSULATORS DO NOT NECESSARILY MAKE GOOD SOUND INSULATORS AND
VICE VERSA.

Pay attention at the back, I never said they did.

The board I am describing is designed to offer good acoustic isolation
as well as reasonable thermal insulation.

It has the cork (high density stuff - about 20mm thick) as one layer,
and it also is covered on the rear side in a thick bitumen backed foil
of the type typically used for sound deadening in cars. The PIR foam
itself in the middle of the board is also pretty good at suppressing HF
noise transmission. Each block also has significant mass compared with
most insulating only materials.

Since this is an internal wall, thermal insulation is IRRELEVANT..unless

You want to have rooms at different temperatures - for example a bedroom
beside a bathroom as in my picture. Or where one room is subject to high
solar gain and the adjacent one not, or when you may want them on
different heating zones to match different patterns of use.


--
Cheers,

John.

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