This work reports the effects of nanoclays and aluminium hydroxide (ATH) on the thermomechanical properties of an unsaturated polyester resin. Dynamic mechanical thermal analysis in the temperature range from 25 to 150 °C has indicated the formation of different structures for the different clay (1, 5 and 10 wt. %) and ATH loadings (50 and 100 wt. %) investigated. The rubbery modulus increases with nanoclay and ATH content which indicates that both nanoclays and ATH act positively on the final network density and consequently lead to systems showing higher stiffness at higher temperatures. The mechanical loss peak value decreases with either nanoclay or ATH content which seems to indicate that both nanoclays and ATH improve network density. The glass transition temperature and the mechanical loss peak value changes linearly with ATH content.