Insulating Concrete Forms use an insulating material as permanent formwork that becomes a part of the finished wall. All ICF's can be considered 'green' materials; they are durable, produce little or no waste during construction, and dramatically improve the thermal performance of concrete walls.
When selecting an ICF system, we recommend the following:

• Specify ICFs with high post-consumer polystyrene content, if any.
• An ICF system that does not necessarily require additional finish materials.
• ICFs that incorporate mineral fiber rather than polystyrene to eliminate a (small) potential source of toxic emissions during fires.

Standard concrete is a dense material with a high heat capacity, which can be used as a ‘thermal mass,’ to reduce the energy required to maintain comfortable interior temperatures. However, concrete is not a good insulator, standard formwork is waste-intensive, and toxic materials are frequently used to separate formwork from the hardened product. Insulated concrete forms (ICF) address each of these weaknesses. ICFs, which use an insulating material as permanent formwork that becomes a part of the finished wall, eliminate wood waste, form assembly and removal, and form-releasing chemicals. The result is reduced solid waste, air and water pollution, and potentially reduced construction cost. Thermally superior ICF wall systems are useful for passive heating and cooling; comfort is enhanced and energy costs are reduced while first costs can be reduced by reducing HVAC system size. A myriad of materials are used for ICF systems, such as lightweight foamed concrete panels, rigid organic foams like expanded polystyrene, and composites that combine concrete with mineral wool, wood waste, paper pulp, or expanded polystyrene beads. Rigid organic foams used in ICFs generally do not have significant recycled content and are less likely to be recyclable at the end of their life, but may be reused in fill or other composite concrete products.

ICFs offer the structural and fire-resistance benefits of reinforced concrete; structural failure due to fire is rare to nonexistent. Due to the addition of flame-retardant additives, polystyrene ICFs tend to melt rather than burn, and interior ICF walls tend to contain fires much better than wood frame walls, improving fire safety overall. Most ICFs are covered by relatively fire-resistant gypsum board, so burning possessions and finish materials are likely to be a more significant hazard to occupants and fire personnel. Rastra tends to be still more fire resistant than standard ICF because the polystyrene in Rastra blocks is encapsulated in cement, a feature that can be very handy in fire-prone areas. There are also ICF systems that substitute strawbales or fiber-cement for polystyrene, such as BaleBlock and Faswall.

As with any heated structure, moisture control is a key design consideration for ICF walls. Solid concrete walls sandwiched in polystyrene blocks tend to be very well sealed (enhancing energy efficiency), but they consequently also tend to seal water vapor within the structure. Potential mold growth and impaired indoor air quality are serious health concerns, and remediation generates solid waste, so (as with any well sealed construction technique) mechanical ventilation is often necessary. Systems such as strawbale and Rastra tend to be more vapor permeable, reducing this concern. Consult with your building official and design professional to determine requirements for your structure.

For More Information:

U.S. Office of Energy Efficiency and Renewable Energy Building Technologies Program

Prescriptive Method for Insulating Concrete Forms in Residential Construction (Second Edition)

Oak Ridge National Laboratory –Moisture Control Handbook
In Adobe Acrobat format. Click to download (17.8 MB).

Rastra

GreenSpec
A fee-based service searchable by the standard UniFormat. It is probably the most comprehensive single source of green building product information.

Oikos
A free website with information about a wide range of greener construction products

Center for Resourceful Building Technology
A free website with information about a wide range of greener construction products

EPA Environmentally Preferable Purchasing

Ready-mix suppliers usually offer at least one type of insulated concrete form, usually polystyrene ICFs. For example:
Granite Rock