AbstractIn‐service secondary creep rates of natural rubber (NR) vulcanizates at ambient temperature are known to be low. However, in tests on thin strips of NR vulcanizates in tension, secondary creep at rates of up to 120%/week were observed. From an examination of the effect of antioxidants, antiozonants, waxes, and specimen thickness it was shown that the anomalous creep was due to ozone attack on the vulcanizate, which only becomes serious in tests on thin strips in tensio