Knowledge of the specific equilibrium heat of fusion of polymer crystals, Delta h(f)(0)[J/g], is an essential thermal property of polymers which permits the degree of crystallinity to be obtained from thermal measurements. We describe an approach to evaluate Delta h(f)(0)(T-m) and implement this method using fast scanning calorimetry (FSC). Our method uses the measured enthalpy of melting plotted against the product of the sample mass times its crystallinity for samples with variable masses and/or crystallinities. Then, Delta h(f)(0) is obtained from the slope of the entire data set, reducing errors in the measurement. To demonstrate the method and give proof of principle, we measure Delta h(f)(0)(T-m) of samples of a narrow fraction of linear polyethylene (PE) with a weight average molecular weight of 60,700 gimol, whose thermal properties are already known in the literature. For PE, we obtain Delta h(f)(0)(T-m) = (281 +/- 6) J/g at T-m = 136 degrees C, in close agreement with literature values. Then, we apply the method to determine Delta h(f)(0)(T-m) of silk fibroin, a fibrous protein, yielding a first estimate of the heat of fusion of silk crystals, Delta h(f)(0)(Silk) similar to (137 +/- 7) J/g. Advantages include: reduction of error, applicability to all types of polymers, copolymers, and blends regardless of degree of crystallinity, and applicability to biomaterials which may require fast scanning rates of FSC to prevent degradation. (C) 2017 Elsevier Ltd. All rights reserved.