Any finite element analysis of the steady peeling of a flexible backing in which the pressure-sensitive adhesive (PSA) acts in a rubbery manner requires stress-strain data to describe the elasto-plastic behaviour of the adhesive. If these are obtained from experiments on bulk or macroscopic specimens then the measured values must be adjusted to account for the additional constraint experienced by the material when present as a thin adhesive film. Modelling fixed-arm peeling of a commercial tape consisting of an aluminium backing bonded with an acrylic PSA as a plane strain problem with these adjusted adhesive material values leads to predictions of peel geometry, peel force and de-adhesion energy. These predicted values have been found to be satisfactorily close to those measured in fixed arm and mandrel peel tests.