1. But neither overgrips nor lead tape nor dampeners are required to play tennis either, yet I don't think they are considering banning any of those. Yes, strings are required to play tennis, yet they banned spaghetti strings anyway for producing too much spin. So why won't they also ban poly strings for producing too much spin? 2. But the string by itself only has one coefficient of friction (COF). Only when you introduce another material to be in contact with the string can you have different coefficients of friction. But you can't increase the roughness of a string and thereby increase its COF when in contact with the ball but AT THE SAME TIME decrease its roughness to decrease its COF with the same rough strings in the crosses. Either both COFs go up or they both go down. You can't make a surface rougher and smoother at the same time as people are saying about rough strings (i.e., that they give more friction on the ball but less friction on the same cross strings). 3. It's common practice for people to say a certain material itself has a high COF or a low COF when compared to another material even without specifying the other materials it comes into contact with because we assume that the third material is a constant. It's like saying that the shag carpeting in your living room has a higher COF than the granite countertop in your kitchen. No need to specify the exact material they come into contact with because in almost all cases, the rough shag carpeting will have a higher COF than the smooth granite countertop. That's why people get "rug burns". 4. Why would a rough string snap back with greater force than a smooth string? If two strings of the same composition are strung at the same tension, they should snap back at the same force because the "snap back force" is a function of the tensile force on the string. If anything, the terminal snap back force of the rough string will be less than that of the smooth string because with the rough string some of the snap back force is dissipated in overcoming the higher frictional forces of the rough string sliding on rough string.