Product Description DMT insulation backing on 64-66 A body AC heater boxes. Insulates between heater / AC box and firewall. There were no AC heater boxes before 64.NOTE: This piece is already included in the AC heater box rebuild kit. 1964 64 1965 65 1966 66 Barracuda, Dart, Valiant AC heater boxes Materials3/4" matte faced yellow fiberglass insulation. Exact same shape as OEM ShippingFirst Class Mail. We combine shipping.