A stackable insulating foam panel which has a top side and a bottom side. Each of the panels has a median row of alternating projections and recesses with a similar complementary shape. The median row is disposed between two coplanar edge surfaces. Each projection of the top side is opposed to a recess of the bottom side whereby the top side and/or the bottom side of the panel can be interconnected with either the top side or the bottom side of a like panel. The present invention also concerns a wall form assembly which comprises opposed foam panels disposed in parallel relationship to make a wall form for receiving a flowable material such as concrete and a plurality of connectors for tying the opposed foam panels together.