The above article demonstrates a diminishing return on “R” value – showing that once a true R25 is achieved – additional R value has diminishing returns. If no preview available – please click pop out in upper right corner.
Above is another study that shows how R values in framed walls are misleading, and in fact perform at much lower levels than stated. If no preview available – please click pop out in upper right corner.
Expanded polystyrene actually increases in R value performance at lower temperatures! If no preview available – please click pop out in upper right corner.
The above study measures the Performance Value of Structural Insulated panels vs conventional walls.