quasi more or less got it, they are rolls of coated steel (called simply, 'steel coils'). I don't know what they are coated with. you can see see several other steel coils in the background. These 3 coils total just over 41,000 lbs, the front 2 weighing roughly 15,000 lbs each and the back one 11,000 lbs. They are loaded near the center of a 48' step-deck trailer. Hauling steel coils is alot of work, beginning with setting the dunnage in place, you can see the front of a 'coil rack' by the front coil, before these were invented you would have to use more wood and build a cradle for them, this load required 9 chains and binders, and had to be fully tarped. the whole process from backing into the loading bay to finishing tarping and ready to leave the plant was roughly 90 minutes.