Three higher hydrocarbon phase change materials (PCMs) with melting points of 25, 40 and 50 degrees C were microencapsulated by in situ polymerization of amino-aldehyde resins. Trimethylolmelamine (TMM) and hexamethoxymethylolmelamine (HMMM) were studied as amino-aldehyde prepolymers for microcapsule wall formation, in combination with emulsifying/modifying agents based on styrene-malein anhydride copolymers (SMA) of different molecular weights and different styrene-maleic acid anhydride ratios. Microcapsule sizes, size distribution and wall permeability were analysed. A mathematical model was developed for comparing the mechanical resistance of different batches of microcapsules, produced at different TMM-SMA ratios. Larger microcapsules with thicker walls and larger pores (M-LAR) expressed lower resistance to breakage than slightly smaller microcapsules with thinner walls and finer pore structure (M-SMA). Mathematical data were confirmed by a smudging colouration test. Laboratory microencapsulation process parameters were optimized to obtain impermeable microcapsules with improved mechanical stability. The process was transferred into a 101 pilot reactor for two PCMs with melting points of 25 and 40 degrees C. Dry powder of microencapsulated PCMs was obtained by spray drying of aqueous microcapsule suspensions.