143: Why is foam such a good building material?

RL Adams PlasticsMany people have concerns about using foam (polystyrene) because of the chemicals used to make the stuff. In fact some of those chemicals are on the Living Building Challenge Red List. So why is foam such a good building material?

Foam is a Great Insulator

It’s all about R-value. Foam is an incredible thermal insulator. For the price, it’s about the best insulation material you can get for it’s size.

Using foam boards in place of building wrap reminded me of Aridon
Using foam boards in place of building wrap reminded me of Aridon

RL Adams Plastics came to my attention with news of a ‘new Home Barrier System’ in the middle of 2015. I was intrigued. It looks similar to the New Zealand product Aridon (see episode 37) because it acts as a weather barrier as well as a layer of insulation.

This is exciting and relevant to home building in New Zealand and Australia for two reasons;

  1. We don’t insulate very well
  2. We don’t do airtightness (or even weathertightness) very well
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RL Adams Plastics

Curtis VanDyke is Director of Product Development & Building Products at RL Adams Plastics, Inc. He shared with me what makes their particular product special, and the steps they’ve gone to in order to make foam as green as possible.

Polycore foam from RL Adams is just one of their innovative foam building products
Polycore foam from RL Adams is just one of their innovative foam building products

Foam is a good building material

Foam is lightweight, relatively cheap and can be formed to almost any shape. As a flat sheet, such as Aridon or Adams’ Fan Fold product, this can double as a weather resistant layer as well as a continuous insulation layer, which can dramatically cut down thermal bridging through the building frame.

It’s also good to know that companies like RL Adams are working hard to make these petrochemical products as ‘green’ as they can, helping to make foam an even greater building material.

For more on making foam ‘green’ check out this post on Green Building Advisor.

  • It seemed like your guest referred to Polysterene as something different to EPS (expanded Polysterene) – what was he referring to? XPS (extruded Polysterene)?

  • mcutlerwelsh

    Here’s a response from Curt regarding EPS and XPS:

    POLYSTYRENE is XPS = eXtruded polystyrene foam…typically a dense closed cell material

    EPS = expanded polystryene foam….typically an open cell material, thus less dense; spaces between the little white beads of foam.

    It is a known fact that EPS (white bead foam) does not wick away moisture very well which can produce unhealthy results when installed while damp inside or behind siding of wall material. Some EPS manufacturers laminated film on both sides of the material, however, if the material is cracked or split during the installation process it opens up for even more moisture retention. Unfortunately for the homeowner, many times the siding is installed over this condition without their knowledge.

    Whereas, our polystyrene foam (XPS) does not retain moisture due to the closed cell material and has the natural ability to wick away moisture and no matter what “damage” may occur during installation, the material will not retain moisture.

    I also encourage anyone with questions to visit our website http://www.goadams.com to learn more about our products and view some of our educational videos.

    Hope this explanation helps!



    • Polystyrene for insulation is a great thing but using it to construct a quality house need STRUCTURAL Materials that requires a Foam EPS that can be coated with a Thin-shell Concrete and XPS fails that task.

      • mcutlerwelsh

        Impressive image. Why can XPS not be coated? Are there not composite products where XPS has a coating or board bonded to it?

      • It comes down to how each is manufactured. EPS is expanded with Water XPS with SOLVENT which produces a different Cell Structure. ZPS also has a tough Skin on panel surfaces that is great for glueing metals and other materials but Concrete see this Skin as a Mold Release surface.

        EPS has larger cell openings XPS has tiny irregular openings that seem to cause the problems. Here is a couple more links that add some to the solution and problem



        Concrete Polystyrene Composites require a Concrete surface to resist Fire, UV, Water, Abuse, but for Builders of Energy Efficient Buildings it’s hard to find an easier system to use. http://bit.ly/1NZyjll