Abstract: An insulation assembly for insulating elongated wall, ceiling, floor and roof cavities having standard widths and nonstandard widths less or greater than standard widths for such cavities, includes a series of elongated insulation modules separably joined together and having widths less than the standard cavity width for the cavities to be insulated. Preferably, each of the modules are compressible and resilient in the direction of their widths and include a fibrous insulation encapsulated within a plastic film envelope. An insulation panel, having a width approximating the width of the cavity to be insulated, is formed by separating a selected number of one or more modules from the series of modules. The insulation panel is then inserted into the cavity and secured in place to insulate the cavity.