An XPS insulation board is specified by three numbers — density in kg/m³, thickness in mm, and compressive strength in kPa — and a buyer who locks all three against ASTM C578 Type IV/V/VI avoids the most common 2026 field failure: foam that crushes under slab screed or delaminates from a torch-applied membrane.
Extruded polystyrene (XPS) is a closed-cell foam manufactured by continuous extrusion of polystyrene resin with a blowing agent, giving it the water-resistance and compressive strength that open-cell EPS cannot match. In the 2026 China-mill market surveyed through Okorder listings, standard architectural XPS panels are produced at 45 kg/m³ density with effective panel widths of 950-1150 mm and foil-face thicknesses of 0.4-0.6 g (i.e. the laminate mass per unit area, not the foam thickness), in three-layer composite form [S4].
Density and Compressive Strength: The 32-45 kg/m³ Spec Floor
ASTM C578 Type IV XPS specifies a minimum compressive strength of 25 psi (≈172 kPa) and a minimum density of 1.55 lb/ft³ (≈24.8 kg/m³); Type V raises compressive to 40 psi (≈276 kPa) at ≥1.80 lb/ft³ (≈28.8 kg/m³); Type VI hits 60 psi (≈414 kPa) at ≥1.80 lb/ft³ [S4].
The 45 kg/m³ grade common in China-mill export listings sits well above the C578 Type VI floor, which makes it a safe default for inverted-roof and under-slab use where point loads from ballast or screed exceed 100 kPa. Buyers who try to economise by stepping down to 32 kg/m³ should confirm the foam still meets Type IV — anything below roughly 25 kg/m³ falls outside the standard and is typically a rebadged EPS board-core product, not a true extrusion.
Thickness, Width, and Edge Profile Options
Common architectural thicknesses for wall and roof XPS are 20, 25, 30, 40, 50, 75 and 100 mm; widths are 600 mm or 1200 mm depending on market, with shiplap or straight-edge profiles available on most production lines [S4].
China-mill effective panel width for the foil-faced three-layer composite variant runs 950-1150 mm, with variable length cut to container fill — typically 1200, 1500 or 1700 mm increments — and 10-15 day ex-works lead time on standard colours (red, blue, yellow) [S4]. For below-grade use under a 100 mm slab, ≥50 mm single-layer is the engineer preference; a 2 × 50 mm staggered-joint build-up is often cheaper than 100 mm single-layer in some regional price bands and gives redundant moisture barrier.
Skin Types: Plain, Foil-Faced, and Three-Layer Composite
Plain (skinless) XPS is the cheapest and the right pick for buried applications where no thermal gain from a reflective face is possible; foil-faced XPS (typically 0.4-0.6 g aluminium laminate) adds a radiant barrier and a vapour-retarder function but must be protected from alkali in direct contact with wet concrete [S4].
Three-layer composite panels — steel sheet faces with an XPS core — are a different product line used for prefabricated cold-store and cleanroom wall assemblies, not for cavity-wall insulation. Buyers comparing these against PU vs EPS spec bands should note that the three-layer panel cost is dominated by the metal skin, not the foam, so direct $/m² comparisons against plain EPS or PU are misleading. For an honest density/price cross-check on the foam-only category, the EPS board price and cost guide 2026 lays out the parallel bodyboard-blank vs insulation board pricing logic.
Fire Behaviour, Blowing Agent, and Code Constraints
Standard XPS is rated Euroclass E (or ASTM E84 Class C in US listings) and produces toxic smoke when burning — it is not a fire-stop material, and facades over 18 m in many EU jurisdictions require a non-combustible cladding (Euroclass A1/A2-s1,d0) over the foam, per EN 13501-1 classification logic. [S1]
Modern XPS uses HCFC-free blowing agents (typically CO₂ or a hydrocarbon blend) following the Montreal Protocol phase-out; older stocks of HCFC-142b-blown foam have higher GWP (Global Warming Potential) and are restricted in EU and California markets. For projects chasing LEED v4.1 or BREEAM credits, request the mill's EPD (Environmental Product Declaration) — the 0.4-0.6 g foil laminate also affects the recyclate stream and should be declared separately from the foam [S4].
Selection Criteria: XPS vs EPS vs PU vs Mineral Wool
On four decision criteria — water absorption, compressive strength per unit cost, lambda value, and fire rating — XPS, EPS, PU and mineral wool line up as follows for typical 2026 projects: water absorption: XPS < PU < EPS < mineral wool (XPS best); compressive strength per dollar: EPS > XPS > PU > mineral wool (EPS best, but only at the same density); lambda (W/m·K): PU ≈ 0.022-0.024 < XPS ≈ 0.029-0.033 < EPS ≈ 0.033-0.038 < mineral wool ≈ 0.035-0.040 (PU best); fire rating: mineral wool A1 > PU E (with treatment) > EPS E > XPS E (mineral wool best). [S2]
The takeaway is structural: pick XPS where water and compressive strength dominate (inverted roof, parking deck, basement perimeter), pick PU where lambda per mm dominates (cold store, low-thickness refurbishment), pick mineral wool where fire dominates (high-rise facade, acoustic partition), and pick EPS where cost dominates on a dry structural application. The same PU vs EPS spec logic applies — XPS is the third leg of that stool, not a substitute for the others.
Sourcing Reality 2026: China Mills, MOQ, and Lead Time
Okorder-listed China XPS exporters quote 45 kg/m³ foil-faced panels at effective widths 950-1150 mm, 0.4-0.6 g foil, red/blue/yellow colour options, 10-15 day delivery, and carton or bubble-pack export packing [S4].
Lead time is the 10-15 day figure once the order is confirmed — add 25-35 days for ocean freight to North America or the EU from Shanghai or Tianjin, so realistic project planning is 6-8 weeks from PO (Purchase Order) to jobsite. For buildings combining XPS perimeter with a concrete admixture spec under the slab, co-ordinate the two deliveries to share container slots and cut freight.
Two signals worth tracking into late 2026: (1) tightening of EU F-Gas-like regulation on XPS blowing-agent GWP, which would push prices on CO₂-blown foam up if the regulation is extended; (2) container-freight volatility out of North China ports, which has historically swung delivered XPS prices by ±15% quarter-on-quarter through 2024-2025 — request a freight-pass-through clause in any mill PO signed before August 2026.