Up to nine crews fought the fire at its height in Hurst Business Park, Navigation Drive.
Smoke was seen rising from the industrial unit at around 4.40am on Friday.
Around 50 firefighters worked to quell the flames at the factory thought to be P Patterns Ltd.
The remained at the scene conducting checks and investigating the cause for almost 10 hours until around 3pm.
Six crews were initially sent by West Midlands Fire Service but they quickly sent a further three to the scene as the scale of the blaze unfolded.
Half of the building has been affected by fire with four crew members wearing breathing apparatus in order to get close enough to tackle the flames.
Crews from Brierley Hill, Haden Cross, Dudley, Stourbridge, Tipton, Woodgate Valley, Smethwick, Oldbury and Handsworth attended.
Later relief crews from Wolverhampton, West Bromwich, Oldbury and Northfield attended.
The Hazard Area Response Team from West Midlands Ambulance Service are currently supporting the fire services at the scene.
WMAS Hart tweeted: "The team are supporting our West Midlands Fire colleagues at a large commercial fire Navigation Drive, Brierley Hill."
An investigation continues into the cause.