Type I ccSPF typically can be used for interior
applications where the temperatures and humidity are
more moderate. Type II ccSPF can be used in more
extreme temperatures and humidity such as cold storage
facilities, mushroom farms, and swimming pools. Type
III ccSPF is used in exterior applications such as roofing
and exterior tank insulation. Type IV ccSPF is fairly rare
but would be used where the foam requires exceptional
impact resistance such as heavy foot traffic or severe hail
ASTM D 2126; Standard Test Method for Response of
Rigid Cellular Plastics to Thermal and Humid Aging is
used determine the dimensional stability of foam plastics.
It measures the volume change of a sample when exposed
to high heat and humidity. In most cases the foam sample
expands, although it can shrink. The resulting change in
volume is reported as percent volume change in a linear
(cont’d on the next page)
Shrinking Foam &
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How incorrect dimensional stability can prevent SPF from performing correctly
Type I 15 psi 12%
Type II 25 psi 8%
Type III 40 psi 6%
Type IV 60 psi 4%
One of the more common issues I run across in my consulting business is shrinking or contracting closed-cell spray foam (ccSPF). This is where the foam shrinks from a stud creating a gap between the stud and the foam. This gap can prevent
the spray foam from performing effectively as an air
barrier, reduces its insulation effectiveness, and can create
conditions that lead to condensation.
So what is the connection between shrinking foam and
dimensional stability and why is it important?
All foam plastics expand or contract to some degree. This
expansion and contraction is referred to as dimensional
stability. It is important to have the correct dimensional
stability for the application. For example a ccSPF that
works well in a cold storage application may not perform
as a roofing product.
SPFA in its technical guidelines and educational courses
refers to ASTM C 1029; Standard Specification for Spray-
Applied Rigid Cellular Polyurethane Thermal Insulation
based primarily on compressive strength and dimensional
stability for the different types of foam used for various
applications, explained in the table below. Poor dimensional stability
can cause ccSPF to
contract from the studs.
In some cases, the
contraction can be severe.
Shrinking ccSPF can
warp and crack drywall