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 pre-polymers 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 10l 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.