Warmalite i think the brand name is but Wickes have 'polystyrene veneer' it's a roll of polystyrene costs �2.14 at our local wickes and covers 58 sqft it's 30ft in length, i have used it before it lasted about 4 years and i'm about to redo mine, you need to make sure the wall is sized first then using the premixed paste put it on the walls then either line or wallpaper over, only thing is when you press against it it can dimple, but it makes it nice and warm, have you tried getting a deumidifier? and the best solution is the cavity wall filling if your property is suitable, makes a massive difference like The builder says.