What even is upholstery? 
It is the covers of furniture.  This includes the padding, springs and fabric
Ahh okay, that's kinda what I thought it was.
The word actually comes from the Middle English.  It means upholder
That makes a lot of sense as to the root of it.
Upholstry has changed a bit in modern times.  It often uses sythetic material like vinyl and acron
That outta be a lot cheaper and easier to produce.
I would imagine it is much easier.  Earlier times it was all done by hand, each layer, using straw, hay, linen, etc