Mackerel nuggets used in this study were coated with HPMC prior to battering or coated with batter containing HPMC in order to improve crust crispness through the formation of a thermal gel barrier preventing the diffusion of water from meat into the crust during microwave reheating. A physical properties assessment and sensory analysis showed that S- and SH-pattern products exhibited a firm and brittle texture, while W- and WC-pattern batters exhibited crispy crust texture. Water molecule diffusion from fish meat into the crust was inhibited during microwave reheating in HPMC-coated products. Nevertheless, a slight toughness was observed in HPMC-coated products still hot following microwave reheating. This may relate to the thermal gelation HPMC film adhering to the crust. Nonetheless, HPMC's ability to serve as a barrier to water diffusion effectively improved the crispness of HPMC-coated mackerel nuggets that had been reheated in a microwave in comparison with non-HPMC-coated nuggets.