Unstabilized poly(ether block amide) (PEBA, PEBAX) of the type used in angioplasty balloons was aged at temperatures of 18–85°C for periods of up to 313 days. Since PEBA is used in safety critical applications, understanding the effects and underlying mechanisms of ageing and the validity of accelerated ageing protocols is vital. Mechanical testing indicated an increase in modulus during ageing consistent with embrittlement. An activation energy (Ea) of 47.3 kJ mol−1 was calculated over the temperature range 18–45°C and increased deviation from linear Arrhenius behavior observed above 45°C. This value of Ea would result in the commonly applied 10°C rule over estimating shelf life. Fourier Transform Infrared Spectroscopy, Gel Permeation Chromatography, and thermal analysis provided evidence that the observed property changes were largely the result of oxidative damage and crystallinity effects. The data presented provides a rational basis for the use of accelerated testing protocols at temperatures of up to 45°C to generate room temperature shelf life estimates.