Polyiso is a very good insulation material. We commonly referred to it as ISO; the molecule that makes polyiso is polyisocyanurate. We are going to look into insulation R-value of polyiso. Below you will also find a ‘Polyiso R-Value Thickness Calculator’ (insert inches, get ISO R-value) and ‘ISO R-Value Thickness Chart’.
Here is the key metric we have to know in order to calculate the thermal resistance capability of ISO:
Insulation R-value of polyiso is R-5.8 per inch of thickness (typically). You can also see polyiso boards with R-value as low as R-4.8 and as high as R-6.5
If you compare the R-value of polyiso to other materials in this insulation R-value chart, you will see that polyisocyanurate has above-average insulation capabilities. That’s why we use polyiso in several insulation types (you can also check all types of insulation here), including:
- Polyiso rigid foam or polyiso foam board. In the industry, we refer to these boards as ISO boards. ISO boards have a thickness from 0.5 inches to 2.5 inches, with a corresponding R-value of R-2.9 to R-14.5.
- Polyiso insulating concrete forms. These concrete forms can increase the R-value of walls up to R-20.
- Polyiso structural insulated panels (SIPs). Here polyiso foam boards are placed between two oriented strand boards. We use 4-inch polyiso SIPs with an R-value of R-12 and 8-inch polyiso SIPs with an R-24 insulation value.
Using polyisocyanurate R-value per inch, we can calculate what is the R-value of any polyiso thickness. To help you out with this calculation, we have designed ‘Polyiso R-Value Thickness Calculator’. Basically, you just insert how many inches of ISO you are using, and the calculator will determine the R-value of that thickness of polyiso.
Below the calculator, you will also find the ‘ISO R-Value Thickness Chart’ that specifies what R-values different thicknesses of polyisocyanurate have.
Let’s start with the calculator and then proceed to the all-important chart:
Polyiso R-Value Thickness Calculator
R-value ISO calculator is quite easy to use. Let’s solve two example to see how it works:
Example 1: What is the R-value of 2 inches of polyiso? You just slide the slider in the calculator to ‘2’ inches and you get the result: 2-inch polyiso board has an R-value of R-11.6.
Example 2: Let’s say that we have a very thick 8-inch ISO board. What is the R-value of 8 inches of polyiso? You just slide the slider in the calculator to ‘8’ inches and you get the result: 8-inch polyiso board has an R-value of R-46.4.
Here are calculations for 1-inch to 20-inch thick ISO boards, summarized in the polyisocyanurate R-value thickness chart:
ISO R-Value Thickness Chart
|1 Inch Polyiso||R-5.8|
|1.5 Inch Polyiso||R-8.7|
|2 Inch Polyiso||R-11.6|
|2.5 Inch Polyiso||R-14.5|
|3 Inch Polyiso||R-17.4|
|3.5 Inch Polyiso||R-20.3|
|4 Inch Polyiso||R-23.2|
|4.5 Inch Polyiso||R-26.1|
|5 Inch Polyiso||R-29.0|
|5.5 Inch Polyiso||R-31.9|
|6 Inch Polyiso||R-34.8|
|6.5 Inch Polyiso||R-37.7|
|7 Inch Polyiso||R-40.6|
|7.5 Inch Polyiso||R-43.5|
|8 Inch Polyiso||R-46.4|
|8.5 Inch Polyiso||R-49.3|
|9 Inch Polyiso||R-52.2|
|9.5 Inch Polyiso||R-54.5|
|10 Inch Polyiso||R-58.0|
|11 Inch Polyiso||R-63.8|
|12 Inch Polyiso||R-69.6|
|13 Inch Polyiso||R-75.4|
|14 Inch Polyiso||R-81.2|
|15 Inch Polyiso||R-87.0|
|16 Inch Polyiso||R-92.8|
|17 Inch Polyiso||R-98.6|
|18 Inch Polyiso||R-104.4|
|19 Inch Polyiso||R-110.2|
As you can see, if you stack ISO boards one on top of the other 18-inches thick, they will have a combined R-value over R-100. That’s quite an amazing R-value.
Hopefully, now you know a little more about ISO R-values and how thick polyiso you need to use in your situation. If you have any questions regarding ISO R-values, you can use the comment section below and we will try to help you out.
Table of Contents
4 thoughts on “ISO R-Value Chart: Thickness Of Polyiso Insulation (1-20 Inches)”
Will the R-value of poly iso increase by doing multiply layers? Is 5 layers of 1″ a higher R-value than one layer of 5″?
Hello Devin, in theory, 5 layers of 1-inch ISO have the same insulation R-value as one 5-inch ISO layer. Basically, a little bit of air can be captured in between several layers but that shouldn’t have a significant impact on the overall R-value. Hope this helps.
what is the cost for 4″ polyiso insulation for flat roof of 1400 sf
Hi Walter, 4-inch polyiso costs about $1.20 to $1.60 per square foot of flat room. If you have 1400 square feet of flat root, that’s anywhere between $1680 and $2240. So, around $2000. Hope this helps.