An insulating panel attachable to a building, the building defining a building aperture, the building aperture defining an aperture plane extending substantially thereacross. The insulating panel includes a membrane structure defining a first external wall and a substantially opposed second external wall; a peripheral wall extending between the first and second external walls, the first external wall, second external wall and peripheral wall together defining an enclosure; and an internal wall system located between the first and second external walls, the internal wall system being configured so as to divide the enclosure into a first cell located substantially adjacent to the first external wall and a second cell located substantially adjacent to the second external wall, the first and second cells being substantially spaced apart respectively from the second and first external walls by the internal wall system. A frame is attachable to the building, the frame being operatively coupled to the membrane structure for maintaining the first external wall substantially parallel to the aperture plane and substantially in register with at least a portion of the building aperture when the frame is attached to the building.