In standard cone calorimeter test fire response properties like time to ignition, peak mass loss rate, time to peak mass loss rate, average mass loss rate and burn out time are of interest. The ASTM 1354  recommends sample thickness of less than 50 mm for the test. However, for thinner samples conditions on the unexposed side of the sample should represent actual conditions in real-life application as the test results may be affected by these conditions. Therefore, in this work, a numerical study is carried out to predict the effect of sample thickness on the fire response parameters of polymeric materials. Polymeric materials are broadly classified as charring (thermoset) and non-charring (thermos-plastic). A representative material in each category, namely CPVC (Chlorinated Polyvinyl Chloride) for charring polymer and PMMA (Poly Methyl Metha-Acrylate) for non-charring is studied. It was noted that properties like the peak mass loss rate, time to peak mass loss rate, average mass loss rate and time to ignition vary with sample thickness for both charring and non-charring polymer. These property values become constant for sample thicknesses beyond a certain value. The variation in properties is dependent on the condition on the backside of the sample. When an aluminium block was assumed to have been placed below the sample, the property variation was different from when an adiabatic condition was assumed. The fire response properties for charring and non-charring materials also exhibited different trends. © 2021, Springer Nature Singapore Pte Ltd.