A chemical incident unit was called to Swindon on Tuesday night, after a large cloud of black smoke formed over part of the town.
A minor rail line between Swindon and Gloucestershire was affected by the blaze but services continued.
The fire took hold on the Hawksworth Industrial Estate, at Doeflex Vitapol on Newcombe Drive and crews returned early on Wednesday to dampen down.
Extra precautions were taken because PVC granules could have been involved.
Six breathing apparatus and foam jets were used by firefighters.