Thick black smoke from the blaze poured out of the Sheffield Reclaim Ltd building in Attercliffe.
The smoke could be seen as far afield as Worksop, Leeds and Gainsborough.
Around 50 firefighters and 10 appliances attended the blaze on Foley Street from around 2.30pm.
No casualties were reported, and people were advised to go indoors and keep their doors and windows closed.
Commander Rick Rolt said the main fire had been tackled, and the crews were hoping to scale back operations.
He added: “We’re likely to be turning the plastics over and damping down for days but we’ve just got monitor jets on the fire now so we may be able to scale back later.”
“The crews have done an absolutely fantastic job.