Doing a garage conversion ,door has been removed and wall put up half way then a window fitted ..before I fit the window ledge I want to put some insulation in there,cant use kingspan as the ties are in place but looking for some sort of fibre or other type with a good value that I can purchase myself and put in there but looked online and cant find any... I dont want to call a firm in for such a small job 8ft x4ft, any help would be appreciated