The group refractive index and physical thickness of dry and hydrated type I collagen films are measured using optical low-coherence reflectometry. The average value for the group refractive index of dry and fully hydrated collagen films at λo = 850 nm is, respectively, 1.53 ±0.02, and 1.43 ±0.02. The physical thickness of type I collagen films nearly doubles when going from the dry (56 μm) to hydrated (118 μm) state.