"The concrete walls of an ICF home have high thermal mass, which buffers the interior of a home from the extremes of outdoor temperature during every 24-hour cycle. This reduces both peak and total heating and cooling loads.
"This combination of R-values, low air filtration, and high thermal mass is
believed to account for the amazing 25% to 50% energy savings of ICF
versus wood or steel-framed homes."
- Source: Insulating Concrete Form Association