R-Value vs. U-Value

If you’re deciding what windows to include in your structure, or if you’re in the market for replacement windows, it is easy to become overwhelmed by some of the perplexing terms used to describe energy performance. R-Value and U-Value, for example, are two commonly used terms that are especially confusing for the everyday consumer. However, understanding the differences and specific qualities of each one will help you make an educated decision regarding your windows that will surely benefit you in the long run.


R-value measures the product’s insulation and its ability to resist heat transfer. A higher R-value signifies more insulation, therefore that product is more effective at preventing heat from escaping in the winter or entering during the summer.


U-factor describes how well a certain product will prevent heat from exiting the building by measuring the heat transfer itself and indicating the rate in which heat escapes through a particular window assembly. The term is used to describe the performance of the entire system and not just the insulation. A lower U-factor signifies less heat transfer.

Comparing R-Value to U-Value

U-Value is a slightly more complex idea in comparison to R-Value. While R-Value accounts for a material’s resistance to heat flow in regards to conduction, U-Value accounts for how energy enters and leaves the material, therefore it considers convection and radiation in addition to conduction. To put it simply, R-Value measures the resistance to heat transfer, while U-Value measures the rate of heat transfer.

Numerically speaking, U-Value is the reciprocal of R-Value. To determine the U-Value, you will divide 1 by R (U=1/R) and to find R-value, you will divide 1 by U (R=1/U). So, if a material has an R-Value of 4, it has a U-Value of .25. The higher the R-value, the lower the U-factor.

It is important to understand R-value and U-Value in order to choose the perfect window system for your structure. A window’s ability to insulate and reduce heat transfer will subsequentially make it easier for HVAC systems to maintain the building’s temperature, which will help reduce energy costs.

Solar Innovations, Inc. offers the highest-quality glass and polycarbonate structures that are ideal for any climate and will keep users comfortable all year round. If you have additional questions regarding window performance, Solar can guide you through the design process to assure your structure has the perfect window system to suit your needs.