Be careful when you construct your own cable lifters. One of the reasons people use them is to lift cables off the carpet to negate the effect of plastics and other artificial fibers in the carpet. Using plastics and foam in a lifter adds back in what you are trying to remove. If your room is hardwood flooring, or your cable runs travel over natural fiber and vegetable dye carpet, you don't have the problem to start with. Teflon, ceramic, glass, natural wood, carbon fiber -good. Plastic bad.
That being said, there are other reasons than those stated above that people use lifters, including aesthetics.