Perhaps there is air trapped between the layers that can't get out, even under vacuum. When you pull a vacuum however, these trapped bubbles will expand, effectively increasing the spacing and causing the C to drop. Just a thought... - MIke > ... This makes me wonder, because if I pull out the air I must > be reducing the space between the 2 pieces of AL foil (I AM removing air), so > I would expect it to go up, not down.