Can you explain the difference between synthetic and natural grafts for leg bypass?

Vein vs. Symthetic. Typically natural bypass grafts are your own vein or artery. It is also possible to use cryopreserved vein or artery from a cadaver (less common but an option). Synthetic grafts are made either or gore-tex /ptfe or woven polyester (dacron). The natural grafts are less likely to clot when there is poor circulation and they are less prone to infection.
Sure. Natural grafts for a bypass would be to use something like a leg vein to bypass an artery. A synthetic graft is using a man-made graft. Both have advantages and disadvantages. Your surgeon should explain the differences and benefits of both types of grafts.