I have seen several companies selling an additive supposedly made of tiny ceramic beads which are claimed to increase insulation value. Some claim outrageous R-values. Our walls were stuffed with loose insulation in the early 1970's; so I suspect it has fallen to the bottom of the walls due to gravity.....I'm wondering about a break even point outside of tearing out walls and putting in insulation, dry wall, paint, paper, labor...... This of course depends on the validity of the claims of the manufacturers. Google Search finds the following companies: Hy-Tech and Insuladd, which was featured on HGTV a while ago.