The thermal third order nonlinearity of a neutral density glass is measured using the Z-Scan method. The measurements are performed using two different laser configurations: a continuous wave laser at 532 nm and a femtosecond laser at 1060 nm. The measurements are used to determine the nonlinear refractive index, n 2 and the thermo-optical coefficient dt dn of the samples. The measurements in the two different laser configurations are in good agreement with the existing theory models.