def METHOD_NAME(ddtt):
    """
    R value (m2-K/W) of a construction or material.
    thickness (m) / conductivity (W/m-K)
    """
    object_type = ddtt.obj[0]
    if object_type == "Construction":
        METHOD_NAME = INSIDE_FILM_R + OUTSIDE_FILM_R
        layers = ddtt.obj[2:]
        field_idd = ddtt.getfieldidd("Outside_Layer")
        validobjects = field_idd["validobjects"]
        for layer in layers:
            found = False
            for key in validobjects:
                try:
                    METHOD_NAME += ddtt.theidf.getobject(key, layer).METHOD_NAME
                    found = True
                except AttributeError:
                    pass
            if not found:
                raise AttributeError("%s material not found in IDF" % layer)
    elif object_type == "Material":
        thickness = ddtt.obj[ddtt.objls.index("Thickness")]
        conductivity = ddtt.obj[ddtt.objls.index("Conductivity")]
        METHOD_NAME = thickness / conductivity
    elif object_type == "Material:AirGap":
        METHOD_NAME = ddtt.obj[ddtt.objls.index("Thermal_Resistance")]
    elif object_type == "Material:InfraredTransparent":
        METHOD_NAME = 0
    elif object_type == "Material:NoMass":
        METHOD_NAME = ddtt.obj[ddtt.objls.index("Thermal_Resistance")]
    elif object_type == "Material:RoofVegetation":
        warnings.warn(
            "Material:RoofVegetation thermal properties are based on dry soil",
            UserWarning,
        )
        thickness = ddtt.obj[ddtt.objls.index("Thickness")]
        conductivity = ddtt.obj[ddtt.objls.index("Conductivity_of_Dry_Soil")]
        METHOD_NAME = thickness / conductivity
    else:
        raise AttributeError("%s rvalue property not implemented" % object_type)
    return METHOD_NAME