Essential work of Fracture (EWF) analysis was used to study the effect of temperature on fracture toughness of PET film. Using Double Edge Notched Tension (DENT) specimens, it. was found that between +25 degrees C and +80 degrees C, the specific essential work of fracture, w(e), of PET film is independent of temperature, having an average value of 33.40 kJ/m(2). The w(e) value was reduced to 27.51 kJ/m(2) as temperature was raised to 100 degrees C. It is demonstrated that both specific essential (w(e)) and non-essential work of fracture (beta w(p)) terms can be partitioned into two components, one linked to yielding (w(e,y) and beta(y)w(p,y)) and the other to necking/tearing (w(e,nt) and beta(nt)w(p,nt)), of the ligament region. The essential terms, w(e,y) and w(e,nt), were lowest at 100 degrees C, having values of 9.14 kJ/m(2) and 18.57 kJ/m(2), respectively, compared to 14.83 kJ/m(2) and 19.17 kJ/m(2) obtained at 25 degrees C. As for non-essential work tems, it was found that beta(y)w(p,y) decreased with increasing temperature, whereas change in beta(nt)w(p,nt) and beta w(p) values was dependent on the temperature range being considered.