The length depends on how many times it's wrapped around the cylinder.
The arc length of a circular helix is given by:
Let's say we have fabric of 1/2 inch dia. wrapped around a cylinder with dia. 12 inches. What length of tubing will make one complete turn in 20 inches measured along the axis of the cylinder.
The helix is
The radius of the helix is the distance from the axis of the cylinder to the center of the fabric, and the helix makes one turn in 20 inches., where .
The length of the fabric in one turn is then inches.
Does that example help?.