In the US, surgical towels are made from cotton, and are NOT impervious. They are counted items, and should be radiopaque.
Drapes are impervious, and are NOT counted items. Depending on where you are working, drapes can either be made from impervious reusable material, or they can be disposable.
Sometimes, surgeons will use towels to "drape out" the focal point of the surgery.
For example, let's say you are doing a mastectomy. The surgeon will use four towels to isolate, or "square off" the breast. In this case, you would give the surgeon one towel at a time to drape the area. Then the surgeon uses the main drape (the one that covers the entire patient) to create the sterile field.
I spent some time in Nicaragua doing charity surgery. The drapes used in the hospital were made of impervious, non-disposable material. Towels were only used during prep. I can see why you are confused regarding drapes and towels.
In this picture, can you see how small the towels are? These are disposable towels.
Let me know if I can clarify further for you.