Disclosed herein are embodiments of foam backing panels for use with lap siding and configured for mounting on a building. Also disclosed are lap siding assemblies and products of lap sidings. One such embodiment of the foam backing panel comprises a rear face configured to contact the building, a front face configured for attachment to the lap siding, alignment means for aligning the lap siding relative to the building, means for providing a shadow line, opposing vertical side edges, a top face extending between a top edge of the front face and rear face and a bottom face extending between a bottom edge of the front face and rear face.