Graphite Polystyrene (GPS): The Highest R-Value Without the Risk of Deterioration

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Are you in the market for an insulation product and wondering what the best option is?

One of the key metrics you’re likely paying attention to is R-value, but the problem is insulation products are not always as advertised. This is especially true when it comes to true insulation value over the long term.

In this blog post, you’ll see how insulation value actually decreases over time in some of the most popular types of insulation products and how building codes in Canada now mandate that insulation products state this is the case. You will also learn how Halo Graphite Polystyrene (GPS) provides the best R-value without experiencing any deterioration over time.


Why XPS and Polyiso Lose R-Value Over Time

XPS insulation boards stacked ontop of eachotherXPS is typically cited as having an R-value of anywhere between R-4.7/in to R-5/in while polyisocyanurate has an R-value of R6-6.5/in. However, as you’ll see in just a second, building code in Canada now prohibits these products from claiming this because it simply isn’t true.

The problem is with XPS’s long-term thermal resistance (LTTR). In a nutshell, blowing agents deplete over time, reducing XPS’s insulation value over time. The same applies to polyiso.

As such, the newest version of CAN/ULC S701 (the Canadian standard for insulation which is also in accordance with provincial building codes) now recognizes this and requires these insulation products to test and report their LTTR values.

Put another way, manufacturers can no longer claim a “true” R-5/in and reference the standards above.

pink insulation close up product shotAs for XPS loses its R-value over time, it actually has to do with the well-known fact that both XPS and polyiso trap more than just air in their cells – they also trap gas, which depletes over time.

This is a natural process, and while it does provide a higher R-value initially, this isn’t the case long-term. Indeed, these studies are actually misleading because they are only done over a short period of time.

If looked at over a long period of time, air enters into the foam while the gas diffuses out, producing a drop in R-value.

However, the good news is that there are other options on the market.

EPS and GPS (the new standard in thermal insulation), for instance, use air as the blowing agent, which does not lead to a reduction in R-value.

However, GPS offers some advantages over EPS where R-value is concerned.


Why GPS is The Best Option

As we’ve talked about on the blog before, GPS is manufactured just like EPS. However, it also has the added addition of high purity graphite that is infused into the polystyrene beads. This not also reflects and absorbs radiant energy, slowing down the transfer of heat.

The result?

18% more insulation capacity than EPS! Put another way, GPS foam board like Halo insulation delivers a long-term R-4.7 per nomial inch that’s also stable over time, unlike XPS.

Halo exterra insulation product shot


Wrapping It Up

Insulation products aren’t always as they seem, especially when it comes to XPS and its true R-value over time.

In summary, XPS the element responsible for its high initial R-value – blowing agents – is what’s responsible for depleting its R-value when looked at over time.

Products like GPS and EPS use air as the blowing agent, which does not deplete over time. As a result, both of their R-values stay the same over the full lifecycle of the product.



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About the author:
Andy Lennox
President, Logix Brands Ltd.