About R-Values

One of the most commonly asked questions about our product is what is the R-Value of structural insulated panels and how do they compare to R-Value of other types of insulation? While this seems like a fairly simple question, the answer can be complex. As a service to our customers, we have dedicated this page to what we hope will be a comprehensive answer to that question.

The R-Value is a measurement of a materials ability to restrict heat flow. In theory, the higher the R-Value of a material, the better its insulating qualities. However, in practice, there is a lot more than R-Value that determines the performance of a building.

Diminishing Returns. There is diminishing incremental improvement in building performance as R-Values increase. For example, the incremental reduction in energy usage as R-Values increase from 10 to 30 is significantly greater than the incremental reduction in energy usage as R-Values increase from 30 to 50. The graph below illustrates this relationship.

Constant R-Values. The R-Values of certain insulation can change significantly from their advertised R-Values based on conditions such as temperature and humidity. For instance, the R-Value of fiberglass batt insulation declines in proportion to increases in humidity. The foam cores of SureTight structural insulated panels are expanded polystyrene (EPS). The R-Value of EPS is very stable and actually increases somewhat as temperatures decline.

Whole-wall R-Values. Tradionally, wall assemblies are framed with two-by dimensional lumber. While R-Value measures only the insulation at the “center of cavity” and does not take into account the R-Value of the entire wall assembly. Therefore, the actual whole-wall R-Value of a traditionally-framed wall is significantly lower than the advertised R-Value of the insulation in that wall assembly. Note that there are far fewer “thermal short circuits” in a structural insulated panel wall assembly.

Thermal Drift. Certain insulation products can also lose R-Value over time. For instance, some foam plastic insulation materials use blowing agents that have high resistance to heat flow, causing the material to have an abnormally high R-Value at the time of manufacture. But, as the blowing agents diffuse from the cellular structure of the foam over its lifetime, the R-Value of the material is reduced by up to 30%. EPS does not experience “thermal drift” that polyisocyanurate and polyurethane does.

Other Factors. The thermal performance of any building is dependent upon many more factors than R-Value alone. Thermal short circuits, air infiltration, and poor construction are all factors to consider. SureTight structural insulated panels have fewer thermal short circuits and, under testing, have proven to be far more airtight than traditional stick-frame construction.

Neopor®. SureTight, together with our EPS foam core supplier, Opco, Inc. have successfully completed testing an EPS foam core manufactured from Neopor®, an EPS foam bead from BASF. This product has been in wide use in Europe and is being introduced in North America by BASF. Our Neopor® EPS foam cores have nearly 20% greater R-Value than panels made from standard EPS. SureTight structural insulated panels with Neopor® EPS foam cores are available now!

If you would like to learn more about R-Value, here is a good link: www.epsmolders.org/4-rval

  4 ½” SIP 6 ½” SIP 8 ¼” SIP 10 ¼” SIP 12 ¼” SIP
EPS Foam Core 15 - 16 23 - 25 30 - 32 37 - 40 45 - 49
Neopor® EPS Foam Core 18 - 19 27 - 29 35 - 38 43 - 47 53 - 57

The above table presents R-Value in a range based upon R-Value per inch of EPS at 40 degree and 75 degrees of 3.85 to 4.17. The R-Value for Neopor® EPS foam core SIPs is based upon a 17% increase in R-Value versus EPS foam core SIPs.

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