For an insulative material, there is one measurement metric which stands above the rest in importance: the R-value.
Every form of insulation retains heat, but some forms of insulation are better at it than others. In addition, some insulation is more effective in certain climates or in conjunction with certain materials. The R-value is the measurement used to determine how effectively any kind of insulative material retains heat and halts heat transfer. The R-value is measured through a combination of factors, including the insulation’s specific material, density, thickness, how it handles moisture, etc.
In short, the higher the R-value, the more effective the insulation.
A high R-value is not necessary for every home. As designated in the U.S. Department of Energy Graphic on this page, specific regions should incorporate different insulation with varying R-values to fit their specific environmental and climate needs.