These “air permeable” insulation types work by trapping air and must fully fill wall cavities (i.e. contact all six sides of a cavity and leave no air gaps) to be effective; otherwise convective air loops can move through the insulation and significantly degrade its performance. One exception could be TimberHPs' TimberBatt, which claims "flexible, semi-rigid, high density cavity insulation creates wind-tight performance in wood-frame assemblies that can almost eliminate cavity airflow".
For optimal performance, batt insulation must be properly cut and separated to fully fill odd-shaped cavities and fit around wiring and electrical boxes. This can be labor-intensive and so we strongly recommend blown-in or sprayed products, especially in walls.
We discourage low-density (open cell) or high-density (closed-cell) spray foam due to both installation costs and environmental concerns. Spray foam products are not included in these lists but if you are using closed-cell foam, look for products with HFO blowing agents (all open-cell products use water as the blowing agent).
A client of ours building a Passive House in Santa Cruz just installed TimberHP's US-made, wood fiber batt insulation. Price is competitive with rockwool and presumably will come down as the company scales. The CA market is currently served by distributors in Reno, Las Vegas, and Phoenix. Exciting!! Sarah Deeds Deeds Design you've looked into TimberHP's products; any other info to add? Nate Russell Beyond Efficiency FYI-
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