According to the "Tennis Warehouse" (commercial) website (refer to the link, below), "natural gut" is made predominantly from cow intenstines, though sheep intestines were used early on. Since natural gut is very expensive, most players use strings made from artificial materials, such as nylon and other composite materials. Regardless of the source, the process to make strings is basically the same: The material is formed into a single strand via extrusion under heat and pressure, until it meets the requirements of the manufacturer for temperature, tension or torsion, density, gauge (thickness), etc. The string may be colored or left as is (i.e., "natural"). The manufacture will also stamp or laser imprint information about the string on the string itself; often it is so small, that most people aren't aware that it's there. The strands may be cut and packaged into "sets" (i.e., individual packets to string a single racquet, usually 40 feet in length) or "reels" (i.e., a single strand many yards in length which is meant to be cut for individual racquets, usually by a professional stringer). For further information, click on the Wikipedia link, below.
String is made of four basic materials: (1) natural gut-- made form beef intestines (most commonly used material in natural gut) (2) nylon--commonly referred to as synthetic gut. This also covers such terms as multifilament or multifiber (3) Kevlar--also used to produce bullet proof clothing and considered to be one of the most durable of strings but not the most comfortable to play with (4) Polyester -- technically referred to as co-polymer strings. Polyester strings has consistently become the most popular string on the professional tennis tour in the 21st century. On the ATP and WTA tours, natural gut was the most popular string for many, many years. With new technology there are more and more variations of synthetic string available and co-polymer strings are constantly being improved to be more "player friendly". Today, many players are using hybrid string jobs in their racquets. Hybrids consist of different strings in the main (vertical) and cross (horizontal) strings. These can be a mix of various string types or the exact same string material in two different gauges (thicknesses). Still, no man-made string has properties equal to natural gut with regards to how the string responds at tensions between 50-70 lbs, the tesnion range most commonly used in tennis.
From what I've there no such thing as tennis rackets with middle strings made out of coal! I just think people are saying that because they've heard from someone!
Tennis racket strings today are made out of synthetic materials, such as:NylonPolyesterKelvarVectranZyexPolyolefinMetal Wire
the strings in a tennis racquet are simply called "strings".
because they need to have a high tensile strength (the maximum stress an object can handle) so the tennis ball is able to bounce of the nylon strings and so the metal frame can stand the tennis balls energy.
Among the top tennis strings on the market, nylon or polyester string is most often used. Nylon is used in so called monofilament strings; multi-filament feature nylon combined with strings such as polyester, Kevlar, Vectran, etc.
Strings
Babolar revenge polyester strings.
It depends on what you need personally for you. I personally like the Babolot strings, but because they are made of 100% Polyester I do half and half also called the hybrid. The hybrid has two types of strings; in my case the RMP blast and synthetic strings.
Two strings are needed to string a tennis racket. The length of the string is to be about 11 to 12 meters.
It is used to make racket plat
The head of a tennis racket is the entire section of the strings, and the part of the frame that surrounds the strings.
Hitting with flat tennis balls doesn't necessarily hurt your strings all that much, but it definitely hurts your game. They can hurt your strings a little if you are using all of your might to swing into the tennis ball, and because it is flat the ball will flatten out over the strings and cause more areas of the string to become weaker.