The strings that run the length of the racket from the top towards the handle are referred to as the mains. The strings that run from side to side perpendicular to the mains are known as the crosses. A hybrid string job uses different strings for the mains and crosses, rather than the traditional use of the same string for both. There are several different reasons to do this.
The main reason is usually durability. Most times when a string breaks it is one of the main strings. This is due to the higher load the main strings are under during play. Hybrids help solve this problem by using a more durable string for them mains such as Kevlar or polyester, and then using a softer string for the crosses. This setup allows for a durable string set without sacrificing feel and touch. A durability string used all the way around in a racquet will likely feel stiff and unresponsive, but used as a hybrid it will like play much better.
Hybrids are not just for string breakers looking for extra durability. Two strings mixed together usually feel and play much differently than either string alone. Some players like to take advantage of this to help find the exact feel they prefer. The right combination will take advantage of the positive characteristics of each string. Hybrids have been popular among professionals for years. Originally this was for durability, but more recently some players have found hybrid combinations that complement their game more than any one string alone.
I have listed several of the popular hybrid combinations. Any string can be used as a hybrid, but it would be difficult to list every possible combination. I will be happy to string any of the strings I offer in a hybrid setup so don't feel limited to the offerings I have listed. Please contact me for pricing about other possible hybrid combinations.
Cautionary Notes About Hybrids
Hybrids are not for everyone. One of the two strings used is usually something extremely stiff such as polyester. Players with arm problems such as tennis elbow should avoid these strings. The stiffness and vibration from these strings could become quite painful to an already injured arm. Normally two strings of similar properties are not used as a hybrid set since the end result would not be that much different from either string alone. Thus, the required stiff string makes this a bad choice for arm pain sufferers.
The stiffer, more durable string is almost always used as the main string with a stiffer cross string. Several players have asked about reversing the strings and using the softer string for the mains and the stiffer strings in the crosses. Roger Federer employs this practice in his racquets. Although it would be impossible to argue against anything he does, it should be noted this may have disadvantages to most amateurs. The particular combination Federer uses produces incredible spin, but has low durability. This is of little concern to him, but most of us lack the resources to have our racquets strung as frequently. Reversing the strings defeats the main durability advantage of hybrids. Racquets strung this way will last as long as they would if they were strung entirely with the softer string. That said, players who are not frequent string breakers or are not concerned about durability may choose to experiment with this. The prices I have listed for hybrids will be the same regardless of which string is used as the mains. If you want to try this let me know because I will string a hybrid with the stiffer string in the mains unless told otherwise in advance.