GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

Open cell foam shrinking

suect | Posted in General Questions on

Would there be a reason for open cell foam to change in appearance? The foam appears to be shrinking and the fire retardant layer is hard.

There is higher humidity than I would like and a dehumidifier is being used on the main level and attic.

Humidity on main level is between 40-50%. Attic is 50-65%

Consulting with professionals who state they have not heard of this.

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. Jon_R | | #1
  2. suect | | #2

    Thank you. Is there a solution?

  3. Jon_R | | #3

    What is the problem? Appearance shouldn't matter.

  4. creativedestruction | | #4

    "Consulting with professionals who state they have not heard of this."

    If they're the same professionals who installed it, point to the article Jon posted to identify that this is often an installation issue. Properly installed, excessive shrinkage shouldn't occur.

    That said, wood studs and rafters will swell and shrink seasonally with relative humidity changes. Foam doesn't always have enough memory to stay bonded year after year if that humidity swing is too great. This vulnerability is less if the rafter/stud faces are fully encapsulated in foam -- not always possible depending on the assemblies.

  5. suect | | #5

    For the most part the studs are encapsulated. Once not seen, are now become visible.

    One thing I recall about a month prior to this seeing changes. There was a 6” open return only and a fairly significant gap around the fireplace flue, possibly acting as a natural supply, discovered by a HVAC professional while in the attic. He advised to seal both which the rerun was initially done. (Couldn’t find a chimney professional to do this). Could this impact the foam?

    Reason for asking is I had an UltraAire unit installed in the attic. Months later leaking was noticed around the return duct at the plenum. Interestingly the foam appeared more fluffy at that time. Once this leak was sealed the foam returned to the flatter appearance.

    The greatest concern for this question is: will there be longevity to this foam? I’m okay if it is cosmetically so-so, just as long as know it’s performing.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |