Having a thickness made up of four layers or strands.(adjective)
Gnu Collaboartive International Dictionary of English: licensed under The Code Project Open License (CPOL)
Use "four-ply" in a sentence
"Even if a four-ply Scottish sweater feels slightly coarser on the shelf than its French or Italian counterpart, the argument goes, it lasts for decades, arriving at cozy perfection around the time those fancy continental sweaters might start to pill."
"Before long each of us is wearing a four-ply bag vest made of two white ones on the inside and two black ones on the outside."
"One day shopping for "four-ply tires" I asked for foreplay ones."