This tool should be used as a guide only. Hardtop Flexi may not be an exact match for Carbothane 133 HB by but we have given the closest match we can. Hardtop Flexi should do the same job and have similar properties but you should always read the technical data sheets for both Hardtop Flexi and Carbothane 133 HB to be sure. Please see any notes to see any major differences and call us on 01285 862132 if you have any specific questions.