Just a lil better quality/craftsmanship really...plus custom strings are exactly as the phrase states,custom to you..your choice of colors,matierial,serving type etc.some of the newer bow manufacturers are stepping up and using better quality strings these days though..but some are still going the cheapest route,and using lesser grade strings,to wich custom is far more superior because of there matierial used,strand count,time and weight stretched at,serving type used etc..