A method of preventing egress of a vapor from an encapsulated volume can include forming a substantially impermeable vapor barrier along an inner surface of the encapsulated volume. The encapsulated volume includes a permeable body of comminuted hydro carbonaceous material. Further, the vapor barrier can include an insulating layer capable of maintaining a temperature gradient of at least 400° F. across the insulating layer. The permeable body can be heated sufficient to liberate hydrocarbons therefrom and the hydrocarbons can be collected from the permeable body. The vapor barrier layer can be a single or multiple layer construction, depending on the specific materials chosen.