EPO is a PS/polyolefin composite bead: polystyrene stiffness, polyolefin toughness. It gives 90 kPa at 10% strain at 16 kg/m³; EPP needs 20–25 kg/m³ for 50–70 kPa. Choose EPO for rigid, very light parts that are not hit often. Choose EPP when the part is struck repeatedly, runs warm, or needs a burn-rate figure.
We mold both materials on the same steam-chest machines. Figures are typical property ranges for molded parts, not guaranteed limits; what your part reaches depends on geometry, wall thickness and as-molded density.
EPO is a composite bead: polystyrene for stiffness, polyolefin so it does not shatter the way EPS does. It is rigid at the lowest density we mold and recovers poorly from repeated impact. EPP is the reverse.
The EPP and EPO columns of the dataset behind our comparison tool. A wide range is usually a density range, not uncertainty.
| Property | EPP | EPO | What the gap means for your part |
|---|---|---|---|
| Molded density (kg/m³) | 20–66 | 16–33 | EPO reaches the lowest density of any material we mold. If the specification opens with a mass budget, that is where the conversation starts. |
| Compression stress at 10% strain (kPa) | 50–325 | 90–160 | Read against the row above. EPO gives 90 kPa at 16 kg/m³; EPP needs 27–33 kg/m³ to reach 70–100 kPa. EPO is far stiffer per gram, and far more limited at the top. |
| Energy return / rebound (%) | 30 | 25–40 | Close on the number, and the two ranges overlap. Reuse is not decided here but by what is left after the hit: EPP recovers its thickness and can be hit again, while EPO keeps more of the deformation. |
| Long-term service temperature (°C) | 100 | 80 | A 20 °C margin to EPP. EPO meets an 80 °C automotive-industry evaluation basis, which is enough for most interiors but not for engine bays or hot air paths. |
| Minimum service temperature (°C) | −40 | −50 | EPO wins the cold case by 10 °C, matching EPS at −50 °C, so cold-store and frozen-goods handling favours EPO over EPP. |
| Thermal conductivity, W/(m·K) | 0.036–0.042 | 0.037–0.039 | Effectively level and tightly grouped across the three EPO grades. Insulation is not a reason to choose between these two. |
| Feel and rigidity | Semi-rigid: cushions under load, not under a finger | Semi-rigid, harder: stiff without being brittle | The best one-line description of EPO on this page. It is the crisp, board-like feel of EPS without the crumbling. |
| Flame behaviour | GB 8410 ≤70–90 mm/min | No flame rating held; can be modified to reach one | EPP is published with a horizontal burn rate against the automotive interior method and offers flame-retardant grades across the density range. EPO carries no rating as we mold it. |
| Chemical resistance | Polyolefin base: good with acid, alkali, alcohols; not aromatics or chlorinated solvents | 11 of 13 tested media resisted; DBP partial, MEK not resisted | One of the few rows EPO wins outright, and the gap is wide enough to design around. Ketone solvents remain the exception to plan around. |
| Weather resistance | PP tertiary hydrogen triggers photo-oxidation; chalks outdoors within months without additives | PS content inherits benzene-ring UV sensitivity | Neither is an outdoor material as supplied. EPO carries the polystyrene weakness on top of the polyolefin one, so outdoor EPO parts need a deliberate additive package. |
| End of life | Thermoplastic, re-pelletisable, no cross-linking | Thermoplastic, re-pelletisable, no cross-linking | Identical. Both are thermoplastic with no cross-linking, so both can be ground and re-pelletised. |
Same dataset, all thirteen materials
EPO at 60× expansion molds at 16 kg/m³ and gives 90 kPa at 10% strain. EPP at its lightest grade needs 20–25 kg/m³ for 50–70 kPa: more stiffness at two thirds of the mass, which is what an airframe is buying. The trade is the ceiling: 160 kPa against 325 kPa.
Rebound is close, 30% against 25–40%, so what decides is what is left after the hit: EPP recovers most of its compressed thickness, EPO keeps a compression set of 14.1–15.4%. Ask how many times the foam is hit before it is replaced. Once or twice, EPO; dozens or hundreds, EPP.
EPO and our standard EPS grades both give 90–160 kPa at 10% strain, so impact behaviour decides. EPS is hard and brittle; falling-ball figures for the three EPO grades are 35.5, 46.0 and 35.0 cm. If handling damage is costing you EPS parts, EPO keeps that stiffness for less than EPP.
EPP runs continuously to 100 °C, EPO to the 80 °C automotive-industry evaluation basis: enough for most interiors and packaging, not for an engine bay or a hot air path. At the cold end EPO is ahead by 10 °C, −50 °C against −40 °C, which covers cold-store work.
In our chemical panel EPO resisted 11 of 13 tested media; DBP was partially resisted and MEK not resisted. EPP handles acids, alkalis and alcohols but not aromatics or chlorinated solvents. Near adhesives, coatings or fuels, start from EPO. If ketones or plasticised PVC are in the process, say so at enquiry.
We publish EPP burn rates to GB 8410, the horizontal automotive-interior method: ≤70 mm/min at 54–66 kg/m³, ≤80 at 40–50 kg/m³, ≤90 at 27–33 kg/m³, plus flame-retardant grades. EPO holds no flame rating as we mold it. Tell us which standard you are audited against and we will confirm in writing what the grade holds. Outdoors, EPO needs a UV package specified.
Per kilogram, EPO beads sit between EPS and EPP. Per part EPO often wins: it molds at 16–33 kg/m³ where an equivalent-stiffness EPP part would be heavier, and foam cost follows polymer mass. Tooling is the same for both: one vented aluminium steam chest, priced off the part.
Ten application families and the material we start from. Where a third material fits better, the table says so.
| Application | Start from | Typical density | Why |
|---|---|---|---|
| Drone and UAV airframes, model aircraft | EPO | 16–20 kg/m³ | Rigidity at the lowest density we mold, and enough toughness to survive a hard landing that would shatter EPS. |
| Returnable dunnage and KLT inserts | EPP | 27–50 kg/m³ | Dozens to hundreds of trips. Recovery after impact and dimensional stability are the whole specification. |
| Lightweight structural shells and covers | EPO | 16–33 kg/m³ | Board-like stiffness with a flexural strength of 260–370 kPa, at a mass EPP cannot reach. |
| Automotive energy absorption | EPP | 40–66 kg/m³ | Cabin temperatures, a burn-rate specification, and a core that must still work after a low-speed event. |
| Single-trip structural packaging that gets handled | EPO | 20–33 kg/m³ | The EPS replacement case: same stiffness class, but stiff without being brittle when someone drops it. |
| Appliance and HVAC internals | EPP | 27–50 kg/m³ | Warm air paths above EPO's 80 °C evaluation basis, plus automated assembly and repeat handling. |
| Cold-store and frozen-goods handling parts | EPO | 20–33 kg/m³ | Serviceable to −50 °C where EPP stops at −40 °C, with stiffness that survives frozen handling. |
| Battery module trays and ESS packaging | EPP | 40–66 kg/m³ | Load-bearing, returnable and usually required to hold a flame specification, which EPO cannot as molded. |
| Parts near adhesives, coatings or fuels | EPO | 20–33 kg/m³ | Resistant to 11 of 13 tested media. Plan around MEK and plasticised PVC contact. |
| Surface-critical liners for finished panels | Neither (Beaded EPE) | 24–45 kg/m³ | A third material fits better. Both of these are semi-rigid; Beaded EPE is the one that will not mark a finish. |
EPP is ordered by density grade; EPO by expansion ratio, which sets the density directly. EPP compression is quoted at 10% strain to ISO 844, EPO to JIS K 6767.
| Grade | Material | Density (kg/m³) | Key values | Where it belongs |
|---|---|---|---|---|
| EPO 60× expansion | EPO | 16 | 90 kPa @10% · flexural 260 kPa · tensile 0.28 MPa | The lightest structural foam we mold. Airframes and shells where every gram is argued over. |
| EPO 50× expansion | EPO | 20 | 120 kPa @10% · flexural 340 kPa · tensile 0.38 MPa | The best all-round EPO grade, with the highest falling-ball impact value of the three at 46.0 cm. |
| EPO 30× expansion | EPO | 33 | 160 kPa @10% · flexural 370 kPa · tensile 0.53 MPa | The stiff end of EPO, matching the top of the EPS range while surviving handling far better. |
| 20–25 kg/m³ | EPP | 20–25 | 50–70 kPa @10% · tensile 420–560 kPa | Ultra-light cushioning and dunnage. Softer than any EPO grade at a similar density. |
| 27–33 kg/m³ | EPP | 27–33 | 70–100 kPa @10% · tensile 550–750 kPa | Protective packaging and lightweight parts with strong energy absorption and full recovery. |
| 40–50 kg/m³ | EPP | 40–50 | 130–175 kPa @10% · tensile 800–1000 kPa | Structural cushioning: automotive, handling trays, heavier returnable packaging. |
| 54–66 kg/m³ | EPP | 54–66 | 255–325 kPa @10% · tensile 1050–1350 kPa | Structural and load-bearing parts, well beyond anything EPO reaches. |
EPS gives stiffness cheaply and shatters. EPP gives recovery and heat tolerance but needs more polymer for the same rigidity. EPO gives EPS-class stiffness with enough toughness to be handled.
| EPS | EPO | EPP | |
|---|---|---|---|
| Density (kg/m³) | 20–30 | 16–33 | 20–66 |
| Compression at 10% strain (kPa) | 90–160 | 90–160 | 50–325 |
| Energy return (%) | 5–15 | 25–40 | 30 |
| Service temperature (°C) | 75 | 80 | 100 |
| Minimum temperature (°C) | −50 | −50 | −40 |
| Behaviour on impact | Hard and brittle, crushes once | Stiff without being brittle, survives handling | Deforms, absorbs and springs back repeatedly |
On the compression row EPS and EPO look identical. Two rows below they are not: EPO returns two to three times as much energy and takes a drop without shattering.
The rule we use: single trip and cost-led, EPS; rigid, very light, handled by people and hit once or twice, EPO; repeated impact, returnable, warm or burn-rate specified, EPP.
If the pair above is not quite yours, one of these is.
| Comparison | The decision it settles |
|---|---|
| EPP vs EPS foam | Recovery against cost. Whether the part is struck once or many times, and whether insulation or reuse leads the specification. |
| EVA vs EPP foam | Soft conforming contact against structural load. Whether the foam touches a surface or carries it. |
| EPP vs ETPU foam | Elastomer resilience at around 200 kg/m³ against all-round cushioning at 30. What the extra polymer mass actually buys. |
| EPP vs Beaded EPE foam | Rigidity and repeated impact against soft wrap, surface safety and service down to −70 °C. |
| All thirteen, ranked | Every material sorted on each of the seven properties that settle a spec. |
| EPE vs Beaded EPE foam | The same polyethylene shaped two ways: what the forming route costs and buys. |
| Cut vs molded foam | Which forming process the part needs: shape freedom and seams against tooling commitment. |
EPO is a PS/polyolefin composite bead foam: a polystyrene phase for stiffness with a polyolefin phase for toughness. Against EPP it is stiffer per gram: 90 kPa at 10% strain at just 16 kg/m³, where EPP needs 20–25 kg/m³ to give 50–70 kPa. It recovers far less from repeated impact, though. Energy return is close, 25–40% against 30% for EPP, while EPO keeps a compression set of 14.1–15.4%. It tops out at 160 kPa where EPP reaches 325 kPa.
For handled parts, usually. EPO and our standard EPS grades both deliver 90–160 kPa at 10% strain, but EPS is hard and brittle with almost no elastic deformation while EPO is stiff without being brittle, with falling-ball impact values of 35.0–46.0 cm across its three grades and energy return of 25–40% against 5–15% for EPS. EPO also molds lighter, down to 16 kg/m³. It costs more than EPS and considerably less than EPP at the same stiffness.
Because it is the stiffest thing we can mold at almost no weight. At 60× expansion EPO molds at 16 kg/m³ and still gives 90 kPa at 10% strain with 260 kPa flexural strength, and it survives hard landings that would shatter EPS. EPP is tougher still but needs more density for the same rigidity, which on an airframe is mass you have to fly.
EPP runs continuously to 100 °C with short excursions higher and is rated down to −40 °C. EPO meets the 80 °C automotive-industry evaluation basis at the top end and is rated to −50 °C at the bottom. So EPP owns the hot cases (engine bays, appliance air paths, sealed containers), while EPO has the better cold margin for cold-store and frozen-goods handling.
EPO, measurably. In our chemical panel EPO resisted 11 of 13 tested media, with the plasticiser DBP only partially resisted and MEK not resisted. EPP, as a polyolefin, handles acids, alkalis and alcohols but not aromatics or chlorinated solvents. If your part sits near adhesives, coatings or fuels, EPO is often the better-documented choice, but design around ketone solvents.
Per kilogram EPO sits between EPS and EPP. Per part it is often cheaper than EPP, because EPO parts mold at 16–33 kg/m³ while an equivalent-stiffness EPP part is heavier, and foam cost is dominated by polymer mass. Tooling does not separate them at all. Both are molded in the same steam-chest tool, so the tool is priced off the part rather than off the bead.
You do not have to name a material. Send the mass budget, the drop case, how often the part is handled and how warm it gets. We come back with a material, a density and a sample plan, usually within 48 hours.