Filling in hole in wall. Insulation question?

[5oysterman2]

Morning guys. I am in the process of filling in a hole, that looks like was for a flue. I've done the internal side but while i was clearing out the debris, i reached into the cavity & noticed there was not much insulation i could feel.

The bit i could feel was a loose soft material, so where the flue was there is an area without insulation. The hole was covered just by plasterboard & so that area was cold to the touch, which i assume was because of the lack of insulation in the cavity. Before i do the external side, what's the best/easiest/cheapest way to get some insulation into the cavity? Cheers for any replies

 

[jacko555]

Squirt expanding foam

 

[5oysterman2]

Squirt expanding foam

I assume it won't have a detrimental effect on the insulation already there then?

It's obvious that the previous owner/owners have had issues with penetrating damp & condensation in that area.

When it fills the gap between the walls, is there any chance of future moisture/damp problems coming through?