Which type of insulation has the highest R-Value per inch?

The type of insulation with the highest R-Value per inch is spray foam insulation. This material, particularly closed-cell spray foam, typically offers significantly higher R-Values compared to other types of insulation. The R-Value measures the thermal resistance of insulation, and spray foam can achieve R-Values of around 6 to 7 per inch, effectively providing superior insulating performance.

In addition to its high R-Value, spray foam also expands upon application, filling gaps and ensuring a tight seal against air leakage, which further enhances its insulating properties. This characteristic makes it particularly effective for applications where maximizing thermal resistance in limited spaces is critical.

Other types of insulation, such as fiberglass batt, rigid board, and cellulose, tend to have lower R-Values per inch, generally ranging between 3 to 4.3 for fiberglass batt and cellulose, and around 4 to 5 for rigid board, making them less effective in achieving high thermal resistance in the same thickness compared to spray foam.