External skeletal fixation has been used for the management of fractures of many types of bone. The use of polymeric free-form connecting bars in external fixators has become widely used in veterinary orthopaedics because of its versatile forms of frame construction and its relative low costs. Determining thermal-transfer to trans fixation pins during polymerisation of poly(methyl methacrylate) and epoxy putty polymers used for free-form external skeletal fixation connecting bars is important for avoiding temperatures of more than 47 degrees C, which would cause thermal soft tissue injury. Therefore, thermal transfer to trans fixation pins was measured in vitro during the polymerisation phase of these polymers. We used trocar-pointed pins of different diameters that punctured one wall of a connecting tube, resulting in the tip of the trocar-pointed pin reaching the centre of the tube. The FLUKE (R) VT02 infrared digital camera was then used to measure heat transfer to the pins at 1 or 2 cm from poly(methyl methacrylate) or epoxy putty. The polymerisation temperatures of these polymers yield a potentially dangerous level of heat for soft and hard tissue. This was observed in almost all the experimental conditions tested. On the other hand, epoxy putty transfer to the pins did not cause the temperature to reach 47 degrees C at any time or in any of the setups examined. Poly(methyl methacrylate) did reach more than 47 degrees C and remained at that level for more than 1 min at 1 cm from the polymer. This acrylate exhibited polymerisation temperatures higher than epoxy and its heat transfer to the pins was potentially dangerous if used at less than 1 cm from soft or hard tissue.