The ternary mixtures showed a 32 and 36◦C delay in the onset temperature for the ternary systems based on 1 wt% sepiolite and 2 wt% MWNT (1sep:2CNT) and 10 wt% sepiolite and 0.5 wt% MWNT (10sep:0.5CNT) systems, respectively. An explanation for this improvement in thermal stability may be found by investigating the residual char after cone testing. The 10sep:0.5CNT ternary system was the only specimen that left a continuous char at the end of TGA and microcalorimeter testing (11% char@800◦C, see Figure 5), indicating a synergistic performance between sepiolite and MWNTs.