To facilitate the proper choice of reinforcing materials in both tyre carcass and belt, the mechanical response to dynamic loading has been determined for polyamide 6 and 6.6, regular and HMLS polyester, rayon and aramid (Twaron), The samples used in this study were dipped cords subjected to a simulated cure treatment, The heat generation was calculated directly from hysteresis loops, All results were normalized to equal ply strength, The data are presented such a way that the absolute values ave readily available for all materials and load levels, Aramid reinforcing cords show a very low heat generation at all temperatures - 5 to 15 times lower than that for polyesters and polyamides.