Abstract: Chlorinated olefin polymer compositions having unexpectedly high tensile impact strength values and resistance to ignition and burning are composed essentially of an admixture of (1) a normally solid, linear olefin polymer having a bulk density of from about 22 to about 36 pounds/cubic foot with the individual particles thereof being predominantly in the range of at least 300 to about 800 microns in size, the olefin polymer having from about 1 to about 20 percent by weight of chemically combined chlorine substantially heterogeneously distributed along the outer surfaces of the polymer particles; such chlorine being introduced in the substantial absence of oxygen and at temperatures not substantially exceeding about 90.degree. C. while the olefin polymer particles are maintained in a fluidized bed state; and (2) from about 0.1 to about 10 percent based on polymer weight of antimony trioxide, and, optionally, up to about 5 percent based on polymer weight of certain bromine containing compounds.