The appropriateness of the standard equation of state of a rubber band is studied in an undergraduate laboratory experiment. There are two parts to the experiment: In the first part, a band is stretched at constant temperature; in the second, the band is kept at constant length while heated. The two coefficients in the equation of state of the rubber band are determined in four different ways: numerical differentiation of the data, numerical integration of the data, regression analysis, and linear regression on a ‘‘straight‐line’’ form of the equation of state. The advantages and disadvantages of each technique are discussed. The characteristic constants describing the rubber band appear to vary by up to 15% depending on the technique of analysis employed. The origins of these variations are discussed.