Warp and weft and all that jazz
In woven material such as a towel, the warp refers to the longitude threads that are tightly stretched (or warped) on a beam.
Weft threads (latitudinal and also called filler) are then passed under and over the warp to form the fabric.
Towels are woven on dobby looms, meaning each loom has two warp beams-the ground warp that forms the body of the towel and the pile warp that produces the terry pile or the loop you see and feel.
This warp pile thread is fed in with a huge excess of yarn hence the loops are formed.
The longer the loop the softer the towel and it absorbency BUT they do pick easily and can then unravel.
Commercial towels are made with relatively short loops for long life.