A fire crew remains at Plasgran in Manea Road, Wimblington, more than 16 hours after the incident began on Wednesday afternoon.
Road closures are expected to stay in place until midday, the fire service said.
About 75 firefighters worked into the night to put out the fire.
They also prevented its spread to neighbouring properties.
The incident was scaled down at 2300 GMT, when the fire was brought under control.
An investigation has begun into the cause of a fire which has severely damaged a plastics factory in Cambridgeshire.