Controlled permeability formwork (CPF) can increase concrete durability in the critical cover zone, improve surface appearance, and reduce formwork pressures. The system is comprised of a filter, drain, and structural support. While the concrete is being compacted, air and some of the mix water escape through the form leaving the concrete in the cover zone with a reduced water-cement ratio and significantly increased durability. Site measurements carried out by the Cement and Concrete Association in the early 1980s revealed that pore water is responsible for about 90 percent of formwork pressures. This explains why CPF gives substantially lower formwork pressures.