Many insulation companies in our area have begun to sell hybrid insulation systems. In a standard 2x6 wall, they will spray 1" of closed foam inside the wall cavity and then fill the rest with cellulose. The idea is to get all the benefit of the air sealing, but then to get the rest of the R-value from the much less expensive cellulose. I can foresee many potential building science issues with this, but it's hard to compare to anything out there.

Does anyone have experience with these systems? How do they perform? How is their durability?

Thanks.