I’m planning to put insulation between the floor joists above my low, enclosed, dirt-floor crawlspace.  Is it worthwhile to use a reflective insulation instead of or in addition to standard kraft-faced batts?  We don’t have radiant floor heating, just baseboard. 

If so, what about simple aluminum foil, put between the batts and the flooring?  Cheaper than foil-lined insulation products…

Finally, is a poly vapor-barrier on the dirt-floor worthwhile in a dry climate?  We live in northern New Mexico; very dry except during the summer monsoon, cold winters, summer heat not a problem.  Moisture tends to evaporate real fast, so I wouldn’t expect a problem, but maybe what I don’t know can hurt me…

Thanks.