Which insulation type has the lowest R-value provided in the text?

Vermiculite is the type of insulation mentioned that has the lowest R-value among the options provided. R-value is a measure of thermal resistance, indicating how well a material resists heat flow; higher values represent better insulating properties. Vermiculite, while lightweight and resistant to fire, generally provides less insulating effectiveness compared to materials like perlite, cellular glass, and extruded polystyrene. Each of these alternatives offers superior thermal resistance characteristics, which makes them more effective for insulation purposes in construction projects. Understanding the specific R-values of various insulation materials is crucial for architects and builders when selecting materials that will meet energy efficiency and performance standards in building design.