GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Most durable polyiso brand?

ddbear | Posted in Green Products and Materials on

I am planning to use 2″ to 4″ polyiso for an insulated roof, conditioned attic space for my house in Southern California (with rockwool under the roof between the rafters).  But I’m having a tricky time deciding on which specific polyiso product to spec for the design.  Assuming cost is not a factor, is there a particular brand/type that is considered the best quality, most durable polyiso board?  For example there are several different types offered by Hunter, GAF, DuPont, R-Max, Johns Manville, etc.  I like the idea of increased fire resistance, mold resistance, structural stability, and overall longevity so the polyiso layer might last as long as the concrete roof tiles.  Opinions on the best specific brands, types?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. conor_mc | | #1

    I would also like to have an answer to this. Or atleast any brand to avoid?

  2. Expert Member
    ARMANDO COBO | | #2

    We typically use DuPont or R-Max in the South and SW. I've never had the opportunity to rip-off a roof and see what it looks like after years of installed. I would assume that a Remodeler or a roofer can tell you better, or if you find a place that sells reclaimed rigid foam boards, they maybe able to tell you which brand is better.

  3. Expert Member
    BILL WICHERS | | #3

    I've seen a lot, and it's all about the same as far as different manufacturers go. The only way I know of to get a premium grade of polyiso is to step up to something like Dow's Thermax, or the CI Max version from Johns Manville. Both of these are made to be left exposed without a thermal barrier, so they have a heavier facer on one side and are noticeably more durable. The price difference to go up to these products from "regular" polyiso is significant though, and there is essentially no difference in insulating performance. Note that Dow does claim their Thermax product has better cold weather performance compared to "regular" polyiso though, but I think that's most likely due primarily to their choice of blowing agent, so other manufacturers may well be similar these days.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |