The insulation on the sides serves two functions. It helps the cake rise evenly. It also helps the cake form a thick, dark brown crust on top and below. Compared to store-bought cakes, the crust on mine is too thin and too pale. That's because the sides of the metal pan conduct heat from above and below though not much from the sides. I can't let the cake bake long enough to form the crust properly or the inside would dry out. To get the professional look, the cake must be baked in a bottomless wood frame, without any metal pan.