Rigid foam board insulation in belly..XPS or EPS?

[Jeremy9107]

Have read through a lot of threads about what, if any, insulation to use under floor.

Seems to be many ideas on this but am curious about choice of closed cell rigid foam board. Do you go with the extruded polystyrene (XPS) or expanded polystyrene (EPS)? Have watched videos and read testimonials on both but they are made by the suppliers and the bias is obvious with each pointing out flaws and false claims of the other.

For 2" thickness 4'x8' sheets :
The orange store carries Foamular (XPS). rated R-10 for $32.95
The blue store carries R-tech (EPS). rated R-7.7 for $21.99

What are other pros/cons of each? Would love to hear from anyone who has installed either as to their experience over time. Or anyone who uses either routinely.

[AL’ UM- MONEY]

I can't help you because I did not do any research. However I am heading out to the shop now to start installing two inch pink form boards that came from the Orange store. I usually purchase from the blue store but they only had one inch in stock so that was the deciding factor. Mine cost $36.00 per sheet so it seems you got a better deal. I'm redoing a 1969 31 foot sovereign and bought a case of liquid nails and a box of 21/2 screws to hold it in place. Not sure if this is the best method but after pulling a nasty belly pan and awful fiber glass on my back my patience is less then when I started so I hope this will work out.

[Jeremy9107]

Personally (having no expert knowledge) I like the pink stuff better. But I have access to the R-Tech for less than $10 per sheet. Thinking the lower R value is worth the savings but want to make sure it's not a far inferior product in other ways.

[blickcd]

I used the 2" XPS, which was green, and came from the 'blue store'.

My trailer is a rear bedroom and I installed this insulation from the holding tank enclosures all the way back to the rear cross member.

As far as the difference in R-value goes, I don't think that matters a whole lot so go with the cheaper option. Consider that the installation process, piecing it in between outriggers and frame members, and leaving small gaps where edges meet the frame so any moisture could drain out... Its not perfect and air tight.

That said, having insulation under the floor does make the interior more comfortable and I would say is worth the effort.

[Jeremy9107]

blickcd. Thanks. Happened across some free Polyiso insulation but still debating on whether to use it for under the floor. It has the best R value of any of the rigid foam board types but will absorb water...would prefer the pink or blue extruded polystyrene however. Have read is best to seal all gaps with spray foam, but to your point think it would be best just to get as close to frame and cross members as possible and allow that gap for water escape.