Isocyanates that are typically used, or have been used, as cross-linkers in EPI adhesive systems are based on the following isocyanate monomers: toluene diisocyanate (TDI), diphenylmethanediisocyanate (MDI), hexamethylenediisocyanate (HMDI), 3-isocyanatomethyl-3,5,5- trimethylcyclohexylisocyanate (IPDI) and triphenylmethane-triisocyanate (TTI).