What are insulated concrete forms?

For new construction, pre-insulated foundation panels called insulating concrete forms (ICFs) can simplify the task while achieving superior performance. Sometimes referred to a "permanent forms," ICFs are hollow foam blocks that snap together to create formwork that doubles as insulation. The hollow core is filled with concrete to make a strong, well-insulated wall. There are now dozens of manufacturers.

Answer excerpted from Eric Corey Freed's column, Ask the Green Architect on greenerbuildings.com.