On Sun, 15 Nov 2020 23:03:41 +0000, alan_m wrote:

You can also get real wool insulation but more expensive ...

But very nice to handle and no irritating fibres or dust. It does
shed fibres though.

... and you need a thicker layer.

ICBA to do the research/maths but above 8 to 10 inches of these forms
of insulation you get into the releams of diminishing returns. We've
got 4" of real wool but under 22 mm chipboard which also has some
insulation value. An IR thermometer tells me the ceiling is the same
temp as the external internally insulated with 50mm celotex walls and
an IR camera showed the the same. Internal plasterboard walls are at
most 0.5C warmer...

--
Cheers
Dave.