Extruded polystyrene (XPS) and expanded polystyrene (EPS) look like cousins — both white foam, both for insulation. On site they behave very differently, and the wrong pick quietly costs you water, height or load capacity. Here is how to choose without the marketing.
How they are made (and why it matters)
XPS is extruded in a continuous process that closes almost every cell, giving a dense, uniform, closed-cell board. EPS is beads of foam fused together, leaving a more open, bead-textured structure. That single difference drives everything below.
The properties that decide the job
| Property | XPS | EPS |
|---|---|---|
| Water uptake | Very low (closed cell) | Higher (open bead joints) |
| Compressive strength | High, graded 150–700 kPa+ | Lower, varies widely |
| Thermal conductivity | ~0.030–0.034 W/m·K | ~0.035–0.040 W/m·K |
| Cost | Higher | Lower |
| Best use | Wet / load floors, inverted roofs | Dry walls, void fill, budget |
Where XPS wins
- Under-slab and basement floors where ground moisture is constant — closed cells shrug off water.
- Inverted (protected-membrane) roofs where the board sits above the waterproofing and is exposed to rain.
- Load-bearing floors — pick the compressive grade (e.g. 300 kPa for domestic, 500–700 kPa for traffic/garage).
- Underfloor-heating builds — pair with XPS boards and dry UFH panels for a low, warm floor.
Where EPS is fine (and cheaper)
- Internal dry-lining where moisture never arrives.
- Void fill and packaging-style cushioning.
- Budget acoustic or thermal upgrades in protected spaces.
If water can reach it or a load will sit on it, specify XPS and name the compressive grade. If it is dry and static, EPS saves money without a performance loss.
Specifying XPS without guessing
- Density / compressive strength — match to traffic: 150–250 kPa light, 300 kPa domestic floor, 500+ kPa garage/industrial.
- Thickness — 20–100 mm; thicker raises R-value and build height.
- Fire rating — confirm the masterbatch class (e.g. B1/E) for the application.
- Edge profile — shiplap or tongue-and-groove for continuous, gap-free layers.
Frequently asked questions
Is XPS waterproof?
It is highly water-resistant thanks to closed cells, not buoyant like open foam. It is the right choice where the board stays wet or buried.
Which is better under floor heating?
XPS — its low conductivity and compressive grade hold heat in the floor and survive the load, especially in dry (no-screed) panel builds.
Why pay more for XPS?
You pay for closed-cell water resistance and graded compressive strength. In dry, unloaded walls EPS does the same job cheaper.
What compressive grade for a garage floor?
500–700 kPa. Domestic living floors are fine at 250–300 kPa; always spec the grade, not just 'XPS'.
Does thickness change R-value?
Yes — thicker XPS raises thermal resistance and build height, so balance insulation target against door and threshold levels.
Match the foam to the moisture and the load
TANYTE extrudes XPS boards in graded compressive strengths and thicknesses, plus dry UFH panels built on the same closed-cell foam.
Is XPS waterproof?
It is highly water-resistant thanks to closed cells, not buoyant like open foam. It is the right choice where the board stays wet or buried.
Which is better under floor heating?
XPS — its low conductivity and compressive grade hold heat in the floor and survive the load, especially in dry (no-screed) panel builds.
Why pay more for XPS?
You pay for closed-cell water resistance and graded compressive strength. In dry, unloaded walls EPS does the same job cheaper.
What compressive grade for a garage floor?
500–700 kPa. Domestic living floors are fine at 250–300 kPa; always spec the grade, not just 'XPS'.
Does thickness change R-value?
Yes — thicker XPS raises thermal resistance and build height, so balance insulation target against door and threshold levels.
Match the foam to the moisture and the load
TANYTE extrudes XPS boards in graded compressive strengths and thicknesses, plus dry UFH panels built on the same closed-cell foam.