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Community and Q&A

Polyiso – different facings & factory seconds

Airfix | Posted in General Questions on

I have some local options for factory seconds and reclaimed polyiso. Each have different backings. I have a few options available to me. I’m trying to understand the pros and cons.

1) Reclaimed polyiso – felt faced – a little beat up – 2.5” for $22 per sheet.
2) factory seconds – felt faced – new – 2.5” for $13 per sheet
3) factory seconds – paper & fiberglass faced – new – 2.5” for $16 per sheet
4) New retail – foil faced – 2.5” – IIRC $38 per sheet

I’m looking to use this on exterior walls and exterior roof on a new construction in climate zone 6b.

How risky is it to use factory seconds? I don’t know why they were rejected. It could be size, it could be R rating or it could be something like forgetting to add the fire retardant chemical. I don’t know. The price is attractive but how risky is it?

Taping the seams for option 2 looks like it will work. The felt is new and seems like it would be easy to tape. The reclaimed will be much harder to tape because of edge damage and felt lifting at the edges. I’ve not physically seen option 3 yet but I’d imagine the seams will be easy to tape. Option 4 is easy to tape.

Is there any logic about where I should use each of the backing options? Does it make more sense to use the paper/fiberglass on the walls and the felt on the roof or does it not matter?

For the roof (a hybrid unvented assembly) I could top the reclaimed or factory seconds with an inch of foil faced polyiso to make taping easier. How important is taping the seams on the roof?

For the walls how important is taping the seams when I will have 2 layers with staggered edges? Again I could add a layer of new foil faced for easy taping but in my hybrid wall (exterior foam, interior fiberglass) that reduces the permeability of the foam layer drastically.

Waterproofing – Using the paper/felt on the walls is normal house wrap an acceptable way of keeping the insulation dry? On the roof it seems to make sense to extend the ice and water shield from the upper OSB down the sides of the foam to the structural OSB underneath? What’s the best approach to keeping the insulation dry?


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  1. Expert Member
    Dana Dorsett | | #1

    >"How risky is it to use factory seconds? I don’t know why they were rejected."

    With foil faced goods in most cases it's due to blemishes such as dinged corners or facers, sometimes bubbles where the foil isn't fully adhered. Those aren't a big deal, and it fine to use on walls. On roofs with a nailer deck to protect it from boot-prints it's fine too.

    Felt faced can have similar issues, perhaps harder to detect with a quick eyeball check.

    Most foil faced goods aren't great on roofs due to lower density (about 1 lb per cubic foot) and lower psi ratings, but have a higher R/inch- typically labeled R6/inch, sometimes more.

    Felt faced roofing foam is usually at least 1.5lbs or 2lbs nominal density and are "walkable" (not to be confused with "stomp-able") under a membrane roof, with some resilience against permanent denting. Typical labeling is R5.6/inch or a bit more.

    In US climate zones 5 and higher from a dew point control design perspective derate any of it to R5/inch for hybrid roof insulation where there is fluff under the roof deck and foam up top. In walls with a rainscreen gap built in the foil-faced goods can be assumed to be at least R5.5/inch as long as there is shiny foil facing an air gap.

  2. Jon_R | | #2

    Vapor permeability matters - but how much depends on other details.

  3. GBA Editor
    Brian Pontolilo | | #3


    When you say that you don't know why the foam is considered factory seconds, do you mean that you don't know why yet, or that there is no way to find out? Dents and dings are easily fixed, if they are an issue at all. A problem with the formulation of the foam is an unknown that you may be more cautious with.

    On the walls, can you put your WRB over the sheathing and flash your windows and doors to the WRB? Then the foam can just be a thermal layer. I think it is still a good idea to tape the seams, but if the tape fails for some reason, it's not as much of a concern as if you were using the foam as a WRB (which, I'm sure factory seconds are not approved for anyway). I imagine the roof is less of a concern if you will have a nailer deck over the foam where you will install your roofing underlayment.

  4. Airfix | | #4

    I don’t think there is anyway to find out why they are factory seconds? So the risk is an unknown. The seller states most are over runs from orders but I’ve no way to verify that. I’m not using the foam as a WRB. For the walls I’m using house wrap as a WRB outside of the foam (going with outtie windows).

    The wall construction outside to inside is Boral Siding, rain screen gap. WRB, 2.5” minimum maybe 3” of polyiso (original plan was foil faced but could go with felt or paper - better for permeability but worse for taping). OSB, 2x6 frame with fiberglass bibs in cavity, perhaps a smart membrain then Sheetrock.

    The roof is going to be unvented - asphalt shingles, ice and water barrier over OSB, 6” polyiso, ice and water barrier (?) over structural OSB, 14” TJI rafters with 7” of open cell foam under the deck, Sheetrock.

    Climate zone 6b.

    I’m still wondering which type of facing is the most appropriate for which location and how important taping of the seams is.

    Should I try to get the felt faced for all locations? Is the paper/fiber faced better for my walls where it is protected behind the WRB. Should I use the foil faced on the wall because it’s easier to tape? Does it even matter?

    I guess using an ice and rain on the roof is an air barrier so taping of the polyiso is not as important especially with multi layers of polyiso with offset seams.

    There is not much guidance on what polyiso facing is right for which application.


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