A commercial phenol formaldehyde based resole thermosetting resin supplied by Borden Chemical Australia Pty. was filled with ceramic-based fillers (Envirospheres or SLG) to increase its flexural strength. By performing flexural tests at a range of filler addition levels, the optimal addition level of SLG was able to be determined in terms of workability, cost and performance. The composites obtained were post-cured in conventional oven and in microwaves respectively. It was found that the maximum flexural strength of the microwave cured composites were only 5% lower than those cured in conventional oven when the percentage by weight of SLG was 24%. However, the time required for post-curing was also reduced from 10 hours (in conventional oven) to 40 minutes (in microwaves).