An empirical equation for Young's modulus is proposed. It originates from thermal fluctuations and relates Young's modulus for highly oriented polymers, E, to thermal expansion strain of the segments of macromolecular helices, eT, and to measurement time 7:where Eo is the E value at ET -0, CO is the heat capacity, k is the Boltzmann constant, E , P 0.1, and 70 = (10-'2-10-14)s. The equation may be used for description of the temperature dependences of Young's modulus, E( T ) , at r = constant over a wide temperature range: from cryogenic to melting temperatures. It was shown that