I am going to be adding a window in my box soon and was wondering the thickness that I should use. The box has 2 12" Type R's ported at 32hz. The box is divided into 2 one chamber per sub. I have a 4'x4' sheet of ¼ in. lying around. Its pretty stout I think that it should work. I would like to use this as there are no local shops here that carry over ¼ in. its all special order.