This work throws the light on the variation of the optical and structural properties of high-density polyethylene (HDPE) fibers at different temperatures (0 °C to 50 °C). The experimental data of this work has been done using the optothermomechanical (OTM) device attached to the interference Pluta microscope. The density of HDPE fibers was determined at different temperatures. Gladstone and Dale's equation is corrected to be valid with PE fibers. Both of the shift factor and average work per chain were presented against average refractive index of PE fiber. Two different types of polarization; the induced polarizability and the permanent dipole moment were carried out for PE fibers.