A formulation is disclosed useful for semi-permanent, thermal conditioning and styling of the hair comprising a mercaptosilicone polymer derived from greater than 25 mole percent mercaptosilicone monomer. A method of straightening the hair is also disclosed which comprises the steps of applying the mercaptosilicone polymer formula to the hair and then styling the hair at an elevated temperature with a flat iron to achieve a lasting straight style that remains after more than one shampoo cycle.
