Silica thin films synthesized sol–gel process are proposed as flexible encapsulation materials. A sol–gel process provides a dense and stable amorphous silica structure, yielding an extremely high elastic deformation limit of 4.9% and extremely low water vapor transmission rate (WVTR) of 2.90 × 10⁻⁴ g/(m²∙day) at 60 °C and relative humidity of 85%. The WVTR is not degraded by cyclic bending deformations for the bending radius corresponding to a tensile strain of 3.3% in the silica encapsulation film, implying that the silica thin film is robust against the formation of pinhole-type defects by cyclic bending deformations. Flexible organic solar cells encapsulated with the silica films operate without degradation in power conversion efficiency for 50,000 bending cycles for a bending radius of 6 mm.