a heat shield and blocking disc for use in lens grinding which comprises a carrier layer of flexible optical transparent plastic having transparent adhesive coatings on both sides thereof , one of which is adapted to stick to a plastic lens blank but to be stripped therefrom with a minimum of residue with the other adhesive compatible with the normal alloy used in blocking glass lens blanks , permitting a simpler blocking of plastic lenses and the use of the normal alloy , thereby reducing the cost of the process .