Fibre-reinforced polymer (FRP) composite materials are limited in high temperature applications by the matrix glass transition temperature, Tg. At and above this temperature, significant mechanical performance is lost, and degradation processes accelerated. This research explores the use of internal passages, or vascules, within the laminate to carry a coolant fluid, absorbing heat energy and cooling the material. A custom thermal chamber and four-point flexural test fixture were developed to perform in-situ thermo-mechanical testing. Vascular and non-vascular carbon/epoxy specimens were manufactured, containing arrays of four 1.1 mm diameter vascules. Specimens were exposed to temperatures from ambient to 170 °C (Tg = 200 °C). Flexural modulus varied little with temperature across all tests. Non-vascular specimens at 170 °C showed a reduction in ultimate strength of 21 % compared to under ambient conditions. The presence of vascules caused a small improvement in flexural modulus and strength, due to displacement of a small number of 0° fibre tows further from the neutral axis as a result of the manufacturing process. At 15 L·min−1 coolant flow, vascular specimens showed full retention of strength compared to non-vascular specimens at ambient, demonstrating the potential mechanical performance benefits.