This may appear a stupid question but please ignore my lack of basic building knowledge!! I am currently replacing the window cills into several rooms in my house (1950's, brick, no cavity insulation) whilst I have access to the cavity can I 'stuff' wall insulation of the woollen variety into the cavity? Does it have to be held back against one side as with the board type insulation or does it just fill the cavity - is there a damp crossing problem??? Finally will this have any effect or could it cause more problems than benefits due to the 'partially filled void'?? Any response greatfully recieved.