Previous analysis of vitreous carbon data has indicated that CO formation depends on the coverage of O on the surface. As the surface temperature increases, the surface loses O-atom coverage through desorption of O, limiting CO production. The increased surface area of FiberForm would allow a higher steady-state oxygen coverage compared to vitreous carbon, as desorbing atoms can re-adsorb on a different fiber. Higher O-atom coverage would shift the temperature at which CO production peaks to higher values. Thus, the plateau rather than a decrease observed in the TDprompt flux from FiberForm at a high surface temperature is consistent with a surface-coveragedependent mechanism for CO desorption. The coverage-dependent mechanism for CO desorption is also consistent with the peak observed in the flux of TD-slow1 at 1400 K for FiberForm. The angular distributions of CO at Ts = 1023 K and 1623 K for FiberForm are shown in Figure (Supplementary Material). The TD-prompt and TD-slow1 fluxes can be fit well with a cosinepower distribution, cos n θf, with n = 1.16 and n = 1.02 for TD-prompt and TD-slow1, respectively, at Ts = 1023 K, and with n = 1.07 and n = 0.6 for TD-prompt and TD-slow1, respectively, at Ts = 1623 K. The TD-slow2 fluxes were too small to discern a clear cosine-power distribution.