The best type of insulation for a basement depends on the climate in which the house is situated. Different kinds of insulation have different R-values that determine their thermal resistance; the higher the R-value, the greater the effectiveness of the insulation.
The U.S. Department of Energy has divided the country into zones prescribing insulation types for homes by recommended R-value. For example, a house located in Chicago is situated in Zone 5, indicating that the government recommends an R-value from 49 to 60. Blanket fiberglass insulation, which is one of the cheapest and simplest forms of insulation to install, has an R-value from 2.9 to 3.8 per inch. Therefore, approximately 1 foot of blanket fiberglass insulation would adequately seal in heat in the basement of a house in Chicago.