Rigid foam insulation boards on the North American market split into three structural-foam families — polyisocyanurate (ISO/Polyiso), extruded polystyrene (XPS), and expanded polystyrene (EPS) — with mineral-fibre, foam-glass, and composite panels sitting alongside for higher-temperature or fire-rated niches [S2][S3].
Insulation Depot, a 30-warehouse North American distributor of reclaimed and factory-seconds rigid foam, currently lists stock in those three chemistries across ISO 4'×8' panels from 0.5" through 4.5", EPS 4'×4' and 4'×8' from 1.5" to 5", and XPS 4'×8' from 1" to 3.5" — a thickness range that mirrors the practical envelope where these products compete [S1].
Polyisocyanurate (ISO / Polyiso) — Highest R-Value per Inch
Polyisocyanurate is the dominant commercial-roofing board in North America and posts the highest aged R-value per inch of the three rigid foams, which is why reclaimed ISO 4'×8' panels from 0.5" to 4.5" dominate the inventory listings at distributors like Insulation Depot [S1]. Polyiso is supplied as ISO 4'×8' panels with foil or glass-facer facers, and Insulation Depot currently advertises 25% off 3.5" Polyiso plus 2.6" Polyiso and 3" Polyiso in Baltimore, MD as part of its active stock [S1].
Its performance centre is warm-side, dry applications — adhered and mechanically fastened low-slope roof assemblies over steel or wood decks — where the facer handles the UV/ vapour seal and the foam core does the thermal work. For an overview of how the product family fits in the wider insulation category, see the polyurethane insulation reference.
Extruded Polystyrene (XPS) — Moisture-Resistant Below-Grade Board
XPS is a closed-cell, extruded polystyrene board specified where water exposure and compressive load both matter — foundation perimeter, plaza decks, parking decks, and inverted roof assemblies. Insulation Depot's reclaimed XPS inventory runs 4'×8' from 1" to 3.5" with current "Brand New Factory Seconds" stock advertised in Glasgow, KY, indicating steady production overruns in that thickness band [S1].
The closed-cell structure gives XPS consistent thermal performance after wet cycles and higher compressive strength than typical EPS, which is why building codes and XPS thermal insulation board studies in cold-region permafrost embankments cite it for freeze-thaw durability [S3]. For a deeper material cut, the XPS board spec page covers cell structure, blowing-agent history, and code-listed thickness tables.
Expanded Polystyrene (EPS) — Lowest Cost, Widest Density Range
EPS is a closed-cell, expanded-moulded bead board — lower cost per board-foot than ISO or XPS, and the easiest of the three to cut on site. Insulation Depot lists EPS 4'×4' at 5" (Champlain, NY) and EPS 4'×8' from 1.5" to 3" (Kalamazoo, MI), confirming the geometry still defaults to 4'×8' with a 4'×4' utility size in the distribution channel [S1].
EPS is the workhorse for wall sheathing, EIFS, and geo-foam applications where compressive strength is tailored through density (type I through type XV per ASTM C578). Its R-value runs roughly 3.6–4.2 per inch depending on density, and it is widely used in insulation board applications where reclaimed stock at 4'×4' 5" or 4'×8' 1.5"–3" delivers a cost advantage over new ISO/XPS [S1]. The EPS board encyclopedia entry details the ASTM C578 type grid that specifiers use to pin compressive and R-value targets.
Board-Type Insulant vs. Other Forms: Why Shape Matters
The term "board type insulant" (板状绝热材料) is used in the technical literature to distinguish rigid, planar insulants — phenolic foam board, calcium silicate board, mineral-fibre board, microporous silica board — from blanket, pipe, or loose-fill forms [S2].
Sandwich-type insulation boards built from E-glass/epoxy face skins plus polymeric foam cores have been qualified for cryogenic LNG carrier service, and microporous fumed-silica boards have been issued as Standard Reference Materials for thermal-resistance metrology, both cited as "board type insulants" in the broader literature [S2][S3]. Specifying by form factor is the first cut: a board assumes flat, dimensionally stable geometry, which rules out fibrous batts and pipe sections.
Selection Criteria: R-Value, Moisture, Compressive, Fire
Four numbers decide the fit for a given assembly: aged R-value per inch, water absorption, compressive strength, and fire/smoke rating (flame spread / smoke developed, often plus FM Approval for roofing). The three mainstream rigid-foam chemistries — ISO, XPS, EPS — line up as follows on the dimensions that drive most spec calls: [S1]
ISO / Polyiso: highest aged R per inch of the three (the foil facer also helps the radiant component), faces are vulnerable to puncture and UV, most common on commercial low-slope roofs in 2"–4.5" thicknesses per the inventory range of 0.5"–4.5" listed by Insulation Depot [S1]. XPS: closed-cell, low water absorption, higher compressive than EPS, stocked in 1"–3.5" by North American distributors and used in below-grade and inverted-roof positions [S1]. EPS: lowest cost per board-foot, lowest R per inch, density selectable for any target compressive, stocked in 1.5"–5" with both 4'×8' and 4'×4' sheet sizes — the most flexible of the three on geometry [S1]. The insulation board reference page expands the comparison to include fire-rated mineral boards and foam-glass.
Use Cases and Failure Modes
Roofing (low-slope commercial): ISO dominates because the aged R/inch and FM-approved facer systems fit single-ply and modified-bitumen assemblies; the typical 0.5"–4.5" panel range at 4'×8' shows up across the distributor channel [S1]. Below-grade and plaza deck: XPS, because the closed-cell structure tolerates long-term moisture and carries higher compressive load under slab [S1]. Walls and EIFS: EPS, because the moulded bead structure cuts cleanly and takes a wide range of densities for the same 4'×8' geometry [S1].
Common failure modes are chemistry-specific: ISO loses R-value as the blowing agent diffuses out of the foam over years (the "thermal drift" issue that aged R-value numbers already account for), XPS can be attacked by certain hydrocarbon-based adhesives and should be separated from petroleum-based products, and EPS dissolves in solvent-based adhesives and most petroleum solvents. Sandwich-type insulation boards for LNG service are qualified for cryogenic reliability, but the qualification is geometry-and-core specific — it does not transfer to a standard roof ISO panel [S3].
Standards, Sourcing, and Reclaimed Stock
Rigid-foam insulation boards are commonly specified to ASTM C578 (the standard that defines EPS and XPS types I through XV by density and R-value); polyiso roof insulation typically references ASTM C1289 for faced board classification, with FM Approval and UL listings layered on for code compliance. These are the standards the spec sheets use, but the product family is broader — phenolic foam board, calcium silicate, microporous silica boards, and rice-hull or kenaf-fibre composites all appear in the literature as board-type insulants [S2][S3].
On sourcing, reclaimed and factory-seconds rigid foam has become a steady secondary channel: Insulation Depot states reclaimed insulation runs "typically HALF THE PRICE" of new foam board, the material is "structurally intact and fully functional," and the stock is "LEED credit eligible" — three concrete claims that a procurement engineer can verify against the distributor's inventory feed [S1]. Buyers who need predictable lead times still order new ISO, XPS, and EPS from the primary manufacturers; the secondary channel suits price-driven fill-in. For field use, generic "insulation board" product pages list the same chemistry family — see the insulation board overview for the consolidated spec sheet.
Trackable signals: ASTM C1289 and ASTM C578 revision pipelines, the next FM Approval round for ISO facer systems, and Insulation Depot's quarterly stock refresh across its 30 warehouses (Macon GA, Kalamazoo MI, Lawrence MA, Durham NC, Cookeville TN, Tulsa OK, Dallas TX, San Antonio TX, Champlain NY, Glasgow KY, Baltimore MD) are the live indicators to watch [S1].
Background reading: Truck-Mounted Crane Types and Classifications: A 2026 Spec Map.