2010 TRI/PRINCETON CONFERENCE 147 there is further oxidation of the fi bers, degradation of the 18-MEA layer, a loss of plastic- ity and a drop in break stress. Generally accepted wisdom is that heat is damaging but also effective and allows for faster, more convenient styling. The results in this paper suggest that, for most hair, tem- peratures above 100°C do not provide greater benefi ts, but do produce greater damage. For chemically treated hair, in particular, there may be effi cacy gains for going to 150°C, but not higher. The water present in the hair before treatment is important. As there is considerable evidence that rapidly heating wet fi bers produces damage, the limited ben- efi ts gained from fi bers beings preconditioned in water compared to equilibrating at 65%RH. The window of opportunity for technologies to protect against relevant heat damage is also clear in examination of these data. As consumers choose to use irons at temperatures above 200°C there is a need for products that protect from these treatments. ACKNOWLEDGMENTS Mythili Nori and Carl Gorman (TRI/Princeton) provided critical experimental support. We thank Eric Weeks (Emory) and Trefor Evans and Jöel Coret (TRI/Princeton) for useful discussions. This work was made possible through the generous support of TRI’s member companies. REFERENCES (1) S. B. Ruetsch and Y. K. Kamath, Effects of thermal treatments with a curling iron on hair fi ber. J. Cosmet. Sci., 55(1), 13–27 (2004). (2) R. McMullen and J. Jachowicz, Thermal degradation of hair. I. Effect of curling irons, J. Cosmet. Sci., 49(4), 223–244 (1998). (3) R. McMullen and J. Jachowicz, Thermal degradation of hair. II. Effect of selected polymers and surfac- tants, J. Cosmet. Sci., 49(4), 245–256 (1998). (4) F. J. Wortmann, M. Stapels, and L. Chandra, Modeling the time-dependent water wave stability of human hair, J. Cosmet. Sci., 61, 31–38 (2010). (5) F. J. Wortmann, M. Stapels, and L. Chandra, Humidity-dependent bending recovery and relaxation of human hair, J. Appl. Polym. Sci., 113(5), 3336–3344 (2009). (6) M. Gamez-Garcia, The cracking of human hair cuticles by cyclical thermal stresses, J. Cosmet. Sci., 49(3), 141–153 (1998). (7) H. D. Weigmann, Y. K. Kamath, S. B. Ruetsch, P. Busch, and H. Tesmann, Characterization of surface deposits on human hair fi bers, J. Soc. Cosmet. Chem. 41(6), 379–390 (1990). (8) F. J. Wortmann, M. Stapels, R. Elliott, and L. Chandra, The effect of water on the glass transition of human hair, Biopolymers, 81(5), 371–375 (2006). (9) P. Zuidema, L. E. Govaert, F. P. T. Baaijens, P. A. I. Ackermans, and S. Asvadi, The infl uence of humid- ity on the viscoelastic behaviour of human hair, Biorheology, 40(4), 431–439 (2003). (10) B. M. Chapman, The rheological behaviour of keratin during the aging process, Rheol. Acta, 14, 466– 470 (1975). (11) J. M. Kure, A. P. Pierlot, I. M. Russel, and R. A. Shanks, The glass transition of wool: An improved determination using DSC, Textile Res. J. 67(1), 18–22 (1997). (12) J. B. Speakman, The rigidity of wool and its change with adsorption of water vapor, Trans. Faraday Soc., 25, 92–103 (1929). (13) G. B. McKenna, Mechanical rejuvenation in polymer glasses: Fact or fallacy? J. Phys. Condensed Matter, 15(11), S737–S763 (2003). (14) P. Milczarek, M. Zielinski, and M. L. Garcia, The mechanism and stability of thermal transitions in hair keratin, Colloid Polym. Sci., 270(11), 1106–1115 (1992).