This is a post I post I put up on the ProMaster forum on Feb 27, 2020 for a test I did on seeing how much water various types of insulation used on vans would absorb if immersed in water for 2 hours and for 23 hours.
Summary here – see details below
DOW XPS blue styrofoam 2 inches thick – No apparent films on the surfaces
Weight before = 83 grams
Weight after 2 hrs = 83 grams (+0 g)
Weight after 23 hrs = 84 grams (+1 g)
Polyurethane spray insulation 0.6 inches thick ON STEEL
Weight before = 445 grams
Weight after 2 hours= 449 grams (+4 g)
Weight after 23 hours = 453 grams ( +8 g)
Great Stuff Pro Gaps and Cracks 1 inch thick
This was applied to a 8 by 11.5 inch piece of alum foil
Weight before = 37 grams
Weight after 2 hours = 41 grams (+4 g)
Polyiso rigid foam board with foil faces — 1 inch thick
Weight before = 48 grams
Weight after 2 hours = 55 grams (+7 g)
Weight after 23 hours = 61 grams (+13 g)
RTech EPS white styrofoam 1.5 inches thick
It has alum foil on one side, and a “polymeric film” on the other side to provide “excellent” moisture absorption protection.
Weight before = 43 grams
Weight after 2 hrs = 107 grams (+64 g)
Weight after 23 hrs = 116 grams (+73 )
Plywood 3/4 inch exterior
Weight before = 647 grams
Weight after 6 hours = 862 grams (+ 215 g)
Thinsulate from 3M — 2 inches
Weight before = 44 grams
Weight after 2 hours = 225 grams (after wringing it out)
The Thinsulate literally soaks up water like a sponge as it is very porous.
Full text of the post…
Hi,
So, this is the promised followup on how much water various samples of insulation absorb over a full day immersion.
I added the results for a longer soak (23 hours) and for the GreatStuff foam and just to have a material most of us are more familiar with, I did a 2 hour soak of a piece of 3/4 inch plywood. The new data is edited into the original post below…
Hi Baxsie,
Your writeup brought out the Boy Scientist in me — so, went out to the shop and dug up all the insulation samples I could find, cut them down to a standard size of 8 by 11.5 inches, weighed each sample on a postage scale, soaked them in a bucket for 2 hours, dried them off and weighed them again. Results below, but samples are back in the bucket for a longer soak.
The samples vary in thickness, but the surface areas are close.
All of the samples were immersed in a 5 gallon bucket and weighted down such that they were fully under water. The water temp was 58F. The water depth was 12 inches, so average static pressure pushing water into the insulation is about 0.22 psi. So, this is a really severe test for water absorption — much more so than service in a van. But, it is similar to the ASTM test for insulation moisture absorption.
After the 2 hour soak, I took each sample out, shook the surface water off, and dried with a towel and then weighed.
The samples:
RTech EPS white styrofoam 1.5 inches thick
It has alum foil on one side, and a “polymeric film” on the other side to provide “excellent” moisture absorption protection.
Weight before = 43 grams
Weight after 2 hrs = 107 grams
Weight after 23 hrs = 116 grams
DOW XPS blue styrofoam 2 inches thick
No apparent films on the surfaces
XPS is generally acknowledged to have low moisture absorption
Weight before = 83 grams
Weight after 2 hrs = 83 grams
Weight after 23 hrs = 84 grams
Polyurethane spray insulation 0.6 inches thick ON STEEL
This is a scrap from one of my window cutouts from the van
It was sprayed from a two bottle kit from Home Depot (link below)
The inside surface of this develops a bit of a skin that may reduce water penetration and also makes it harder to dry off the surface moisture before weighing.
Weight before = 445 grams
Weight after 2 hours= 449 grams
Weight after 23 hours = 453 grams
Polyiso rigid foam board with foil faces — 1 inch thick
This is the stuff a lot of people have been using to do their vans.
Weight before = 48 grams
Weight after 2 hours = 55 grams
Weight after 23 hours = 61 grams
Thinsulate from 3M — 2 inches
Weight before = 44 grams
Weight after 2 hours = 225 grams (after wringing it out)
The Thinsulate literally soaks up water like a sponge as it is very porous. It is not meant in any way to stop moisture penetration, but it is said that the fibers do not actually absorb water. So, this test is not very meaningful for Thinsulate, but I had the sample and just decided to soak it along with the rest.
Great Stuff Pro Gaps and Cracks 1 inch thick
This was applied to a 8 by 11.5 inch piece of alum foil
Weight before = 37 grams
Weight after 2 hours = 41 grams
Plywood 3/4 inch exterior
Weight before = 647 grams
Weight after 6 hours = 862 grams
————-
Thoughts and opinions on longer test…
XPS definitely the leader on not absorbing much water — only 1 gram over 23 hours.
Polyiso gained another 6 grams for a total of 13 grams for 23 hours. As RD pointed out, A lot of this is probably getting in the edges of the sample, which have no foil facing. Since these are small samples, they have a higher ratio of edge area to face area than a large sheet would, so more realistic size sheets would likely perform even better. This seems like good performance to me when you consider how severe the test is and that the plywood sample gained 215 grams in 6 hours.
Polyurethane spray foam on steel sample
This is about 0.6 inches of spray foam sprayed onto part of a PM window cutout.
The spray foam only gained a total of 8 grams over 23 hours — a bit better than the Polyiso. Also quite good I think.
Great Stuff Pro Gaps ad Cracks applied 1 inch thick to alum foil.
Showed a gain of 4 grams over 2 hours — so, pretty close to the Polyiso sample.
The Gaps and Cracks (I guess) is made to fill larger cavities, and if you cut a sample of it and look at the cross section the bubbles are fairly large (1/4 inch ish) — I suspect that the Great Stuff with finer bubbles would perform even better?
The Great Stuff seems to perform about the same as Polyiso, so it does not appear that its a moisture weakness in the Polyiso/Great Stuff combo a lot of people use.
EPS styrofoam still surprising to me how much water it absorbs. Reading about it a little, its made from styrofoam beads and while the beads are closed cell and do not absorb much moisture, the spaces between the beads do allow moisture penetration and this may account for the 60+ grams of water absorbed.
I cut each of the samples to see if the inside showed any sign of moisture or of an advancing water front. I did not see any sign of wetness on the sample cross sections except for the plywood. The Great Stuff had large bubbles in the cross sectional cut, but no sign of any moisture getting into them.
Gary