3-in-1 Underlayment

Q: I am installing a Westhollow 12mm thick laminate floor…first time…I’m pretty comfortable with everything, but the underlayment…because it was 12mm, the folks at iFloor indicated the 3 in 1 would be okay for my install – it is on concrete slab and all downstairs. Here’s my confusion. The 3 in 1 has the words printed “this side up” on the plastic (moisture barrier side), meaning the foam is to the concrete. This seemed backwards to me as most guides I have seen indicate barrier, then foam. In a return visit, iFloor told me the manufacturer printed it on the wrong side and the plastic to the bottom.
Fast forward to today and I was walking through Lowe’s, saw the same product and noticed it said “this side up” on the plastic side. The dude at Lowe’s said, when it all comes together as one product you do put the plastic up…
Now I am confused and have not started.
Joe Connelly
A: This is a question that comes up fairly often and let me explain why it can be confusing. When you install underlayment like Cork or Sound 6 which is not a combination underlayment, you will install the moisture barrier, then the underlayment. In the case of combination underlayments you can install the underlayment with either way facing up, but here is why you are seeing “this side up” on the moisture barrier side.
The manufacturers of these types of combination underlayments will make their suggestion of which side should go up based on how they want the seams sealed. Also, one of the reasons why you will install with the plastic side up is that it is easier to install the flooring over the plastic than the foam. Gene D., our commercial contract manager, mentioned that this is similar to scrim on carpet padding or kraft paper and makes the installation much smoother.
In the end, it should matter very little which way you choose to install it; however, I would go the safe route and install based on the underlayment’s manufacturer and put the moisture barrier face up.