Polymerization of resin-based materials leads to temperature rise, caused by the exothermic nature of the reaction and energy absorbed during polymerization. This temperature rise is influenced by intensity of light, composition of resins, and type of light source. This study evaluated thermal insulating properties of four photo-polymerizing pulp-capping agents in primary and permanent teeth. Roots of 80 primary and permanent teeth were removed. Class-I cavities were prepared on the occlusal surfaces of teeth. Materials used were TheraCal LC, Biner LC, ACTIVA BioACTIVE, and Calciplus LC and light sources were 3 M-Elipar and VALO LED. Temperature rise was measured using a J-type thermocouple. Data were statistically evaluated using ANOVA and Tukey`s tests (p = 0.05). VALO LED exhibited significantly lower temperature rise in all groups and temperature rise in primary teeth was significantly higher with all experimental materials (p < 0.05). The highest temperature change was observed in the Biner LC group (3.82 ± 0.58) and the lowest change in the Activa-BioACTIVE group (1.78 ± 0.34). The VALO LED light source caused a significantly lower increase in pulpal temperature compared with the 3 M-Elipar source. All tested materials and light sources maintained pulpal temperature under safe limits, with temperature increases not exceeding 5.5 °C.