There is no single cut-off. EPS at about 2 lb/ft³ and 25 psi (ASTM C578 Type IX) and above is generally called high density. Insulfoam R-Tech goes up to 3.0 lb/ft³ and 60 psi.
EPS Foam Density & Compressive Strength Guide
What density and psi mean for EPS foam
Density is how much EPS is packed into a cubic foot of foam, measured in pounds per cubic foot (pcf). Compressive strength is how much pressure the foam takes before it compresses by 10%, measured in pounds per square inch (psi). Denser EPS is stronger, and it also has a slightly higher R-value per inch.
The EPS used in construction runs from about 1 to 3 pounds per cubic foot, and from 10 to 60 psi. Below you will find the ASTM C578 types and the Insulfoam R-Tech range side by side. Choosing a strength for a slab or roof? See under-slab insulation and EPS roof insulation, or ask us.
The Basics
Density, in plain words
Density is the weight of the foam per cubic foot. More foam per cubic foot means a stronger, stiffer board.
Compressive strength, in plain words
Strength in psi is the pressure that squeezes the foam 10%. A 25 psi board compresses 10% at 25 pounds per square inch, which is 3,600 pounds per square foot.
Pick for the load
Roofs and walls often use lower strengths. Slabs, driveways and heavy floors use higher ones. Your plans or engineer set the number.
EPS Density and Strength Charts
Typical values from two manufacturers. Higher density means higher strength and a higher R-value per inch.
ASTM C578 EPS types (Cellofoam typical properties)
| Type | Nominal density (lb/ft³) | Minimum density (lb/ft³) | Compressive strength (psi) | Flexural strength (psi) | R per inch at 75°F |
|---|---|---|---|---|---|
| Type I | 1.0 | 0.90 | 10–14 | 25–30 | 3.85 |
| Type VIII | 1.25 | 1.15 | 13–18 | 30–38 | 3.92 |
| Type II | 1.5 | 1.35 | 15–21 | 40–50 | 4.17 |
| Type IX | 2.0 | 1.80 | 25–33 | 50–75 | 4.35 |
Insulfoam R-Tech faced EPS, 10 to 60 psi
| Product | Nominal density (pcf) | Compressive strength (psi) | Flexural strength, min (psi) | R per inch at 75°F |
|---|---|---|---|---|
| R-Tech I | 1.0 | 10 | 33 | 3.9 |
| R-Tech X | 1.5 | 15 | 40 | 4.2 |
| R-Tech IV | 2.0 | 25 | 50 | 4.4 |
| R-Tech VI | 2.4 | 40 | 60 | 4.5 |
| R-Tech VII | 3.0 | 60 | 75 | 4.6 |
Sources: Cellofoam EPS typical physical properties and the Insulfoam R-Tech 10-60 PSI technical data sheet. Download the EPS typical physical properties sheet and the R-Tech 10-60 PSI sheet. Typical values, not a specification.
Density and Strength Questions
What is high density EPS foam?
What is the density of styrofoam?
People often call EPS styrofoam. Construction EPS runs from about 1.0 to 3.0 pounds per cubic foot, depending on the strength you need.
What does 25 psi mean?
A 25 psi EPS board compresses by 10% under a load of 25 pounds per square inch, which is 3,600 pounds per square foot. It is a common choice when a slab needs a stronger foam. Your plans or engineer set the requirement.
Is higher psi always better?
No. Higher strength costs more, and a roof or wall often does not need it. Choose the strength your load calls for. If you are unsure, ask us and we will go over it with you.
What is ASTM C578?
ASTM C578 is the standard specification for rigid, cellular polystyrene thermal insulation. It sets minimum density, strength and other properties for each EPS type.
Can you supply custom densities?
Yes. Custom sizes, thicknesses and densities are available through our manufacturers. Request a quote with what you need.
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