the process the powdered rubber is present simply as a mechanically dispersed powder in the slurry the chlorinated natural rubber is an item of commerce available in powdered form in a variety of viscosities as determined in a 20 concentration in toluene the specific volume of the material will generally average around 70 cubic inches per pound it is soluble in toluene xylene aromatic hydrocarbon esters ketones and some other commercially used solvents it is used in the present process in the form of the white granular powder just as it is made and sold particle size is as follows at least 95 passing a no 20 sieve 40 to 90 passing a no 180sieve and 40 passing a no 325 sieve the percentage being by weight of the original mass of particles and the sieves being of the standard screen series u s bureau of standards 1919 the powdered rubber is made by chlorinating a natural rubber to incorporate into the rubber an amount of chlorine of about 50 70 by weight such rubber has particular utility for the use intended by the product of the present invention since it is readily solvent soluble in certain commercial solvents is highly fire resistant and when distributed throughout the final sheet lends itself to the formation of shaped cooling tower fill materials in corrugated and saddle form the amount of the chlorinated natural rubber in powdered form to be added to the slurry will be about 25 by weight of rubber.