Cob Insulation v. Thermal Mass

[spearance]

While insulation is a good thing and so is thermal mass, it seems that you
cannot have both.  If you decided to insulate cob with an air space such as
is typically found in double paned windows, you would lose the thermal
mass.  By separating the outer surface from the inner, you lose the
transfer of heat.  Thermal mass would still be effective using passive
solar but the largest gains would be lost.