Provided is a heat insulating window film including a flexible support, and a fibrous metal particles-containing layer containing fibrous metal particles, in which the fibrous metal particles contain silver or an alloy of silver, an average short diameter of the fibrous metal particles is equal to or smaller than 35 nm and an average long diameter is equal to or greater than 5 μm, and a content per unit area of fibrous metal particles of the fibrous metal particles-containing layer is equal to or greater than 10 mg/m2.