If you’ve ever found yourself standing in the insulation aisle, squinting at R-value charts and wondering why EPS (expanded polystyrene) gets all the attention, you’re not alone. EPS is a solid, budget-friendly choice—think of it as the reliable pickup truck of foam boards. But sometimes you need something with a bit more thermal muscle. So, let’s answer that burning question: **which foam board insulation has a higher R-value than EPS?
Spoiler alert: XPS and Polyiso are the cool kids on the block.
Quick Refresher: What’s EPS Again?
EPS is that white, bead-filled foam board you’ve probably seen in coffee cups or packing peanuts (the non-biodegradable kind that escapes into your garden). It typically offers an R-value of around **3.6 to 4.2 per inch**. Not bad! But when you’re battling a freezing basement or a scorching attic, every decimal point counts.
The Contenders That Beat EPS
1. XPS (Extruded Polystyrene) – The Smooth Operator
XPS looks like EPS’s smoother, denser cousin. It’s often pink (Owens Corning), blue (Dow), or green (various brands). Unlike the bead-filled structure of EPS, XPS is a closed-cell, homogeneous foam. That gives it:
- R-value of about 5 per inch – roughly 25-40% higher than EPS.
- Better moisture resistance (great for basements or exterior foundation walls).
- Higher compressive strength – perfect for under concrete slabs.
Downside? It’s pricier and not as eco-friendly (blowing agents used to be tougher on the ozone, though modern versions are improving). But for pure R-value per inch? XPS wins handily.
2. Polyiso (Polyisocyanurate) – The Overachiever
Polyiso is the star student who shows up with an R-value of 5.6 to 6.5 per inch – that’s nearly double EPS at its best! It’s typically faced with aluminum foil or fiberglass facers, giving it a shiny, almost space-blanket vibe.
Here’s the catch: Polyiso’s R-value drops in cold temperatures. Below about 40°F (4°C), its performance starts flirting with EPS levels. So it’s amazing for roofs, attics, and above-grade walls in mild-to-warm climates, but less ideal for a frozen Minnesota basement.
The Verdict (In Cheerful Bullet Points)
- For highest raw R-value per inch: Polyiso (but check your climate!)
- For consistent performance + moisture resistance:XPS
- For budget-friendly “good enough”: Stick with EPS
A Lighthearted Warning
Don’t be the person who buys Polyiso for a below-grade foundation in Alaska, then wonders why your toes are still cold. And please – don’t try to build a foam board fort and declare it a tiny house. (Okay, do it. But insulate the floor with XPS.)
Final Takeaway
If you need a foam board with higher R-value than EPS, reach for XPS (R~5)or Polyiso (R~5.6–6.5). Your heating bill will thank you, and you’ll have the smug satisfaction of knowing you’ve outsmarted basic polystyrene.
