An insulating liner for an article of clothing includes an insulating layer including an aerogel material and having opposite sides with passages extending therebetween, and a cover encapsulating the insulating layer. The cover includes vent holes aligned with the passages of the insulating layer, and has portions that extend into the passages of the insulating layer from the opposite sides of the insulating layer, with the portions having vent holes therethrough and being sealed about the periphery of the vent holes. A valve may be provided with the liner to allow gas to be withdrawn or expelled from the liner. Methods of forming the insulating liner(s) are also provided.