ASTM C578 Types Explained for XPS Producers

ASTM C578 sorts rigid polystyrene insulation into Types by minimum properties. Extruded polystyrene (XPS) boards fall into five common Types, ordered by compressive resistance: Type X (15 psi), Type IV (25 psi), Type VI (40 psi), Type VII (60 psi) and Type V (100 psi), each with a minimum R-5.0 per inch at 75 °F. EPS has separate Types. The active edition is C578-23.

If your customers buy to ASTM, the Type they name sets your density target, your formulation and the tests your lab must run. This guide explains how the Types work, gives the published minimums with metric conversions, and shows what each Type means for an XPS production line.

What ASTM C578 Covers

ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, covers polystyrene boards, with or without facings or coatings, made either by molding expandable polystyrene beads (EPS) or by extrusion (XPS). Laminated products with a rigid board facer, such as fiberboard, perlite board, gypsum board or OSB, are outside its scope (ASTM C578-23 abstract).

Key points from the published scope:

• Service temperature: the main body covers use from −65 to +165 °F (−53.9 to +73.9 °C).
• Pipe, tank and equipment insulation: Annex A1 adds requirements for service from −320 to +165 °F (−196 to +73.9 °C), and names Types IV and XIII for this use.
• General requirements: the insulation must have uniform density and enough flame retardant to meet the specified oxygen index.
• Specified properties: thermal resistance, compressive resistance, flexural strength, water vapor permeance, water absorption, dimensional stability and oxygen index.

ASTM lists C578-23 as the active edition, with earlier editions back to C578-95 now historical (ASTM store).

How ASTM C578 Types Work

A Type is a set of minimum (or maximum) values that every board sold under that Type must meet. It is not a product recipe, and it does not say how the board is made. Three features matter for a producer:

1. Types are ordered by compressive resistance, not by number. Type X (15 psi) is the lightest common XPS Type and Type V (100 psi) the strongest. Type IV sits between X and VI. Do not read the Roman numerals as a strength scale.
2. XPS and EPS have different Types. In Owens Corning’s July 2025 summary of C578-23, the XPS Types are X, IV, VI, VII and V; the EPS Types are XI, I, VIII, II, IX, XIV and XV. A buyer who asks for “Type IV” is asking for an XPS-level board, even though some EPS Types reach the same 25 psi.
3. The values are minimums for conformance. Typical values on a producer’s data sheet are usually higher, and design values are a separate question; check the current edition of C578 for how it treats them.

ASTM C578 Types for XPS: Minimum Requirements

The table shows the basic minimums for the five XPS Types as published by Owens Corning in its bulletin on C578-23 (publication 10015702-C, July 2025). Compressive resistance is measured at yield or 10% deformation, whichever comes first, with skins intact. Metric values are our conversions.

R-5.00 per inch (h·ft²·°F/Btu per inch) corresponds to a thermal conductivity of about 0.029 W/(m·K). Dimensional stability and oxygen index limits also apply to every Type; the bulletin does not list them, so check the current edition of C578 for the values and the test conditions.

What each XPS Type means for production

• Type X (15 psi). The entry-level board for walls and light-duty uses. It has the lowest density minimum, but it must still meet the same R-5.0 and 0.3% water absorption as the stronger Types. Thermal performance and closed-cell structure, not density, are the hard part.
• Type IV (25 psi). A common general-purpose XPS Type for building insulation. If you plan one “standard” board for an ASTM market, confirm with your buyers whether Type IV is the one they ask for first.
• Type VI (40 psi) and Type VII (60 psi). Boards for applications where the designer needs higher compressive resistance, typically where the board carries loads. Compressive resistance rises with density, so these Types need tighter control of density across the width and thickness of the board.
• Type V (100 psi). The heavy-duty board. Its density minimum of 3.00 lb/ft³ (48.1 kg/m³) is above the 30–45 kg/m³ range of our reference XPS line. If your buyers need Type V, raise it at the requirement stage.

Our reference line range is 30–45 kg/m³, so on density alone it covers the Type X, IV, VI and VII minimums. Density is only a minimum, though: conformance depends on compressive strength, thermal resistance and water absorption measured on your own boards.

ASTM C578 EPS Types: What You Compete Against

EPS producers sell into the same specifications, and buyers compare the two. The EPS Types in the same Owens Corning summary of C578-23:

Two differences stand out. XPS Types require R-5.00 per inch against R-3.10 to R-4.30 for EPS, and allow at most 0.3% water absorption against 2.0–4.0% for EPS. EPS needs a higher density than XPS to reach the same compressive resistance: 25 psi needs 1.80 lb/ft³ in EPS Type IX but 1.45 lb/ft³ in XPS Type IV. These are the arguments XPS producers use in ASTM markets. For the full comparison, including how the two plants differ, see XPS vs EPS.

Why You Must Check the Current Edition of ASTM C578

C578 is revised often: ASTM lists editions going back to C578-95, now historical, with C578-23 the active edition. Limits and Types can change from one edition to the next, so a value taken from an older copy of the standard may no longer apply.

For a producer this has three consequences:

1. Set acceptance limits from the edition in the contract. A buyer’s specification or a building code may name an older edition. Keep a copy of each edition you sell against.
2. Buy the standard. The values in this article come from a published manufacturer summary and are for orientation. Before you set limits in your quality plan, check the current edition of ASTM C578 itself.
3. Test reports should name the edition. A report that says “meets ASTM C578 Type IV” without a year is weaker evidence than one that says C578-23.

Testing ASTM C578 Properties in the Plant Lab

C578 sets the limits and refers to separate ASTM test methods for each property. Check the referenced methods and specimen conditioning in the current edition; the usual set is:

A practical lab for an ASTM-oriented XPS plant has a universal test frame with compression and flexural fixtures, a balance and gauges for density, a water bath for absorption and, if the budget allows, a heat flow meter for thermal resistance. Thermal resistance is the property most affected by the blowing agent and by how the board ages, so test it on boards of different ages, not only on fresh board from the line. For the blowing agent side, see XPS blowing agents.

What ASTM C578 Means for Your XPS Production Line

• Choose your Types before you choose the line. If your market wants Type IV and Type VI, the line, die and calibrator are set for that density and thickness range. Type V is a separate question (see above).
• Thickness. ASTM markets buy in inches: 1, 1-1/2, 2 and 3 in. are 25.4, 38.1, 50.8 and 76.2 mm. Our reference line makes boards usually 20–60 mm thick, and 30–120 mm with an HFC-assisted foaming process where regulations allow. Check the thickest board your buyers need against the blowing agent rules in your market.
• Width. Our reference line covers 600–1200 mm widths; ASTM markets commonly use 24 in. (610 mm) and 48 in. (1,219 mm) widths, so confirm the exact widths in your requirement brief.
• Flame retardant. C578 requires enough flame retardant to meet its oxygen index. HBCD, long used in XPS, is listed for elimination under the Stockholm Convention, so the formula needs an HBCD-free alternative from the first trial.
• Water absorption. The 0.3% limit for every XPS Type depends on a uniform closed-cell structure and intact skins. Cutting and planing can open cells; test boards as sold.

ASTM C578 vs EN 13164

EN 13164 is the European product standard for factory-made XPS. It does not use Types. Instead, the producer declares levels for each property, such as compressive stress at 10% deformation, and the declared thermal conductivity must be supported by testing and factory production control. A board certified to EN 13164 is not automatically a C578 Type, and the reverse is also true, because the test methods and conditioning differ. See our guide to the EN 13164 XPS standard.

FAQ

What are the ASTM C578 types for XPS?

Per the C578-23 values summarized by Owens Corning, the XPS Types are Type X (15 psi), Type IV (25 psi), Type VI (40 psi), Type VII (60 psi) and Type V (100 psi) minimum compressive resistance. All require a minimum thermal resistance of R-5.00 per inch at 75 °F and a maximum water absorption of 0.3% by volume. EPS has its own Types: XI, I, VIII, II, IX, XIV and XV.

What is ASTM C578 Type IV?

Type IV is an XPS Type with a minimum compressive resistance of 25 psi (172 kPa), minimum density of 1.45 lb/ft³ (23.2 kg/m³), minimum R-5.00 per inch at 75 °F and minimum flexural strength of 50 psi, per the C578-23 values summarized by Owens Corning. It is a common general-purpose XPS Type for building insulation. Check the current edition before you set limits.

What is the difference between ASTM C578 Type X and Type IV?

Both are XPS Types with R-5.00 per inch and 0.3% maximum water absorption. Type X requires 15 psi compressive resistance and 1.30 lb/ft³ density; Type IV requires 25 psi and 1.45 lb/ft³. Type IV also has a higher flexural strength minimum (50 vs 40 psi). In production, Type IV usually means a slightly denser board and tighter density control.

Which edition of ASTM C578 is current?

ASTM lists C578-23 as the active edition. Many specifications and building codes still name older editions, and limits for some Types have changed between editions. Set your acceptance limits from the edition named in each contract, and check the current edition before you write your quality plan.

Can one XPS line make all ASTM C578 types?

One line can usually cover several Types by changing density, formulation and line settings, but not necessarily all of them. Our reference line runs at 30–45 kg/m³, which covers the density minimums of Types X, IV, VI and VII. Type V requires at least 48.1 kg/m³, so discuss it with your supplier at the requirement stage.

Planning an XPS Plant for ASTM C578 Markets?

Tell us which C578 Types, thicknesses and widths your buyers specify, and the blowing agent rules in your market, and the line will be configured around them. See our XPS foam board production line for the equipment, and the XPS board plant setup guide for the full planning sequence.

Sources

• ASTM International, C578-23, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation (abstract, scope and edition history): https://store.astm.org/c0578-23.html
• Owens Corning, FOAMULAR & FOAMULAR NGX Extruded Polystyrene (XPS) Insulation: ASTM C578 Types and Physical Properties, Technical Bulletin 10015702-C, July 2025: https://www.owenscorning.com/dms/10015702
• Stockholm Convention, Hexabromocyclododecane (HBCD) overview: https://www.pops.int/Implementation/IndustrialPOPs/HBCD/Overview/tabid/7410/Default.aspx