round in cross section would be to produce the same cross sectional area as that of the actual sample the racquet string of the invention is preferably formed from multiple small diameter polymer filaments twisted together to an effective diameter of about 0 055 inch prior to irradiation this multifilament string exhibits some surface roughness which is desirable in play irradiation of the string is performed in the usual manner by exposing the string to a dose of radiation preferably cobalt 60 radiation the equipment used for this treatment may be similar to that manufactured by general electric company for the desired improvement in physical properties of the string the quantity or dosage of radiation absorbed by the string material should be in the range of 7 5 to 12 5 megarads the irradiation causes crosslinking of the polymer molecules but it has been found that above about 12 5 megarads the network molecular chains become shorter diminishing the tensile strength of the string 10 megarads is the preferred dosage for consistently good results in improving the properties of the material the only noticeable visual change in the string material due to irradiation is a darkening of the color of the string from an almost colorless whiteish color to a deeper light amber color testing of irradiated multifilament strings showed marked changed in physical properties as compared with similarly tested untreated strings and showed a near duplication of similarly tested gut material strings which comprised a plurality of twisted together lamb gut strands in the testing three sample strings of untreated monofilament nylon three of irradiated multifilament nylon and two of.