Detailed knowledge of the behaviour of rocks under thermal stress is essential in a variety of fields such as the exploitation of oil and mineral resources, the geothermal sector, the storage of radioactive liquid waste, or even CO2 capture and storage. Granites are widely studied and exploited in these fields, and they show different reactions to high-temperature and thermal cycles due mainly to their high mineralogical and textural heterogeneity. One of the features that influences the most the thermal response is the porosity. The objective of this study is to evaluate the influence of porosity when these rocks are exposed to different thermal treatments. For that purpose, experiments were carried out on four granitoids selected by their similar crystal size, but with variable mineral proportion and porosity values, ranging from 1 to 6%. Two kinds of tests were performed: i) progressive heating cycles from 90 °C to 130 °C to determine the critical threshold for thermal damage; ii) thermal fatigue with cycles of heating-cooling up to 200 °C. The porosity and the water transport phenomena of the samples were characterised before and after each cycle by the monitoring of capillary water uptake coupled with infrared thermography. This technique allowed to follow the capillary fringe migration during the test and the evolution of the cooling rate index. The direct assessment of the damage was carried out by mercury injection porosimetry, optical polarising microscopy, and scanning electron microscopy. The combination of all the results permitted to establish a link between the evolution of temperature and the modification of porous networks in granitoids. Microcracks appeared distinctly at a temperature between 90 °C to 130 °C for high porosity granitoids whose Quartz/Feldspar ratio was close to 1. For higher temperatures, the low porosity granitoids develop microcracks from the first heating cycle. The porosity then showed a stronger impact on thermal behaviour than the effect of the mineralogy. The results obtained from infrared thermography allowed to detect the strong variations in the microstructure. •The initial heterogeneity of a granite generates a different cracking threshold for the same type of granite.•Repeated heating leads to increasing damage to rocks•The initial porosity and the quartz/feldspar ratio play a role in the thermal behaviour of granite.•Infrared thermography is a promising tool to detect microcracking.