Panel including, in succession, a first rigid board forming the back of the panel, a first thermally insulating layer borne by the backboard, an impervious covering covering the first thermally insulating layer, a second thermally insulating layer which partially covers the impervious covering and a second rigid board covering the second thermally insulating layer, characterized in that it includes a film which covers at least part of the impervious covering which is not covered by the second thermally insulating layer, the film including at least one protective portion and at least one spew portion adjacent to the protective portion, the protective portion and the spew portion being able to be detached from the impervious covering independently of one another.