We manufacture both core types in Tongxiang, Zhejiang: extruded PP honeycomb core and MPP micro-foamed insulation panels. Because we sell both, we have no reason to push one over the other. This guide covers the numbers we use when a truck body builder or RV manufacturer asks us which core to use.
The top-ranking articles on this topic describe the trade-off in words, with no tables, no test standards, no thermal data and no prices. This one gives you the numbers.
Core Properties Side by Side
Values below are typical ranges for standard grades. Honeycomb compression is tested flatwise per ASTM C365 and foam compression at 10% strain per ISO 844 / ASTM D1621. Shear is tested per ASTM C273 and thermal conductivity per EN 12667 / ASTM C518. Always ask your supplier for the batch datasheet; a range on a website is a starting point, not a design allowable.
| Core (typical grade) | Density (kg/m³) | Flatwise compression (MPa) | Shear strength (MPa) | λ (W/m·K) | Moisture behaviour |
|---|---|---|---|---|---|
| PP honeycomb, 8 mm cell | 60-80 | 1.0-1.5 | 0.4-0.6 | 0.06-0.08 (effective) | PP absorbs nothing; water can sit in breached cells |
| MPP micro-foamed PP | 60-100 | 0.4-0.9 | 0.3-0.5 | 0.035-0.040 | Closed cell, under 0.5% by volume |
| XPS foam | 30-45 | 0.25-0.50 | 0.20-0.30 | 0.030-0.034 | Good |
| PU foam (reefer grade) | 38-45 | 0.15-0.25 | 0.12-0.20 | 0.022 new, 0.028-0.032 aged | Slow uptake, λ drifts with age |
| PET structural foam | 80-150 | 1.0-2.0 | 0.7-1.2 | 0.030-0.035 | Good |
| PVC structural foam (80 grade) | 75-85 | 1.2-1.5 | 0.9-1.2 | 0.030-0.033 | Good |
| Aluminium honeycomb | 50-130 | 2-10 | 1.3-5 | Thermal bridge | Corrodes if salt water gets in |
Three things stand out in this table:
- At equal density, honeycomb beats a same-polymer foam in compression. PP honeycomb at 70 kg/m³ reaches 1.0-1.5 MPa, while MPP at a similar density reaches 0.4-0.9 MPa. In a honeycomb, all the material stands vertically as cell walls, exactly where flatwise load goes.
- Low-density insulation foams (XPS, PU) are not structural cores. They are 5-8x weaker in compression than honeycomb, which becomes the deciding factor in floors (see the wrinkling section below).
- Honeycomb insulates poorly. The cells are open voids, so radiation and some convection get through. The effective λ of 0.06-0.08 W/m·K is about twice that of any closed-cell foam.
The Weight Myth: Same Thickness, Almost the Same Weight
Many buyers pick honeycomb "because it is lighter". At equal thickness that is mostly untrue. Here is a 20 mm panel with two 0.8 mm glass-fibre PP skins (about 1.2 kg/m² each):
| 20 mm panel, 0.8 mm GF-PP skins | Core mass (kg/m²) | Panel mass (kg/m²) | vs PP honeycomb |
|---|---|---|---|
| PP honeycomb, 70 kg/m³ | 1.4 | 3.8 | baseline |
| MPP foam, 80 kg/m³ | 1.6 | 4.0 | +5% |
| PVC foam, 80 kg/m³ | 1.6 | 4.0 | +5% |
| PET foam, 100 kg/m³ | 2.0 | 4.4 | +16% |
| XPS foam, 35 kg/m³ | 0.7 | 3.1 | -18% |
Skins make up 60-75% of the panel mass, so the choice of core moves total weight by single-digit percentages. Where honeycomb does save real weight is stiffness per kilogram. Because it holds higher compression and shear at the same density, you can use a thinner or lower-density honeycomb to carry the same load. Bending stiffness grows with the square of the skin spacing, so every millimetre of core you add is cheaper than upgrading the skins.
Not sure which core your spec needs? Send us the panel's job (span, load, target U-value) and we will reply within one working day with a recommendation and a sample of each. Request a core recommendation.How Each Core Fails, and the Numbers That Predict It
Competitor articles list "impact damage" and "debonding" as generic drawbacks. In practice, each core has one dominant failure mode, and each has a formula you can check before you order.
Honeycomb: skin dimpling (intracell buckling)
A honeycomb supports the skin only along its cell walls. If the skin is thin relative to the cell size, it buckles inward into each cell under compression, leaving a dimpled "quilted" surface. That is a cosmetic reject on an RV sidewall and a structural failure on a floor. The classic check from the HexWeb honeycomb sandwich design manual is:
σcr = 2·Ef / (1 − ν²) · (tf / s)²where Ef is the skin modulus, tf the skin thickness and s the cell size. For a glass-fibre PP skin (Ef ≈ 10 GPa, ν ≈ 0.3):
| Skin thickness | 6 mm cell | 8 mm cell | 12 mm cell |
|---|---|---|---|
| 0.3 mm | 55 MPa | 31 MPa | 14 MPa |
| 0.5 mm | 153 MPa | 86 MPa | 38 MPa |
| 0.8 mm | 391 MPa | 220 MPa | 98 MPa |
A GF-PP skin typically fails in compression at around 100-150 MPa, so you want the dimpling stress above that. Our shop-floor rule: skin thickness should be at least 1/15 of the cell size (0.4 mm on a 6 mm cell, 0.55 mm on 8 mm, 0.8 mm on 12 mm). If your design calls for 0.3 mm decorative skins, honeycomb is the wrong core unless you add a scrim layer or switch to a finer cell.
Foam: face wrinkling
A foam supports the skin continuously, so dimpling cannot happen. A foam core instead fails by face wrinkling: the skin buckles in short waves that the soft core cannot resist. A conservative design estimate (Hoff-Mautner form) is:
σwr ≈ 0.5 · (Ef · Ec · Gc)^(1/3)With the same 10 GPa skin and typical core moduli:
| Foam core | Ec (MPa) | Gc (MPa) | Wrinkling stress | Verdict for bending-loaded panels |
|---|---|---|---|---|
| PU, 40 kg/m³ | 5 | 3 | ~27 MPa | Walls and roofs only |
| XPS, 35 kg/m³ | 15 | 8 | ~53 MPa | Walls, light roofs |
| MPP, 80 kg/m³ | 30 | 12 | ~77 MPa | Walls, light floors with spreader layer |
| PET, 100 kg/m³ | 90 | 25 | ~141 MPa | Floors, walkable roofs |
This is why insulated reefer walls happily use PU or XPS, while structural foam-core floors use PET or PVC, which cost 3-5x more. When you ask a low-density insulation foam to act as a floor core, the skin wrinkles long before it reaches its own strength.
Water, fasteners and edges
- Water: PP honeycomb does not absorb water or rot, but if a skin is punctured, water can collect in the breached cells. Freeze-thaw cycles then work on the bond line. Closed-cell foam limits water to the damaged zone. Either way, seal every cut edge, as covered in our fabrication guide.
- Fasteners: Neither core holds a self-tapping screw well (150-300 N pull-out). Hinges, tie-downs and cabinets need potted inserts (2,500-4,500 N) or solid PP hardpoints laminated into the panel. This applies equally to both cores, so budget for it whichever you choose.
Thermal Performance: Where Foam Wins Outright
This is the decision that matters most for RV and cold-chain buyers, and no competitor article puts numbers on it. The values below are core-only conduction; surface films and thermal bridges are excluded.
| Core | λ used (W/m·K) | R at 20 mm (m²K/W) | R at 40 mm (m²K/W) | US R-value per inch | Thickness to reach U = 0.40 W/m²K |
|---|---|---|---|---|---|
| PP honeycomb | 0.070 | 0.29 | 0.57 | R-2.1 | 175 mm |
| MPP foam | 0.038 | 0.53 | 1.05 | R-3.8 | 95 mm |
| PET foam | 0.033 | 0.61 | 1.21 | R-4.4 | 83 mm |
| XPS foam | 0.032 | 0.63 | 1.25 | R-4.5 | 80 mm |
| PU foam (aged) | 0.030 | 0.67 | 1.33 | R-4.8 | 75 mm |
U = 0.40 W/m²K is the ATP class FRC limit for refrigerated bodies. To reach it, a honeycomb core would need to be 175 mm thick, which is not a practical truck wall. That is why our refrigerated truck bodies use MPP insulation and keep honeycomb only for hardpoints. A whole-body K-value also comes out 15-25% worse than these flat-panel figures because of thermal bridges; our reefer panel insulation guide explains that correction.
For RV owners comparing a honeycomb wall to a foam wall: a 40 mm honeycomb wall is about R-3.2 in US units, while a 40 mm MPP wall is about R-6.0. For a three-season trailer, honeycomb is acceptable. For four-season use, it is not. See our RV insulation materials comparison for complete wall builds.
Decision Matrix: Which Core for Which Panel
This is the table we use internally when quoting vehicle and RV programmes.
| Panel | Recommended core | Typical build | Why |
|---|---|---|---|
| Dry-freight truck side wall | PP honeycomb | 15-20 mm, 8 mm cell, 0.8-1.0 mm GF-PP skins | Stiffness per kg; no insulation needed |
| Truck or trailer floor | PP honeycomb, 6 mm cell | 25-30 mm + wear layer or CFRT skin | Point loads, pallet-jack traffic |
| Reefer wall and roof | MPP (or PU) | 80-120 mm | U-value governs; honeycomb cannot reach FRC |
| Reefer floor | Hybrid | 20-25 mm honeycomb or CFRT deck over MPP | Needs both structure and insulation |
| Four-season RV sidewall | MPP or XPS | 30-40 mm | R-value; continuous support for thin decorative skins |
| Three-season or teardrop trailer wall | PP honeycomb | 15-20 mm | Lightest stiff wall; insulation secondary |
| RV floor | PP honeycomb or hybrid | 25 mm honeycomb, or honeycomb + foam layer | Furniture legs and jack loads; see our RV floor guide |
| RV furniture and cabinets | PP honeycomb | 12-15 mm, 12 mm cell | Flat, light, screw-able with inserts |
| Walkable roof | PET foam or 6 mm cell honeycomb | 25-30 mm | Wrinkling and dimpling both need a stiff core |
- If the panel needs U ≤ 0.7 W/m²K, use foam. Honeycomb alone needs 100 mm or more.
- If design flatwise pressure after skin spread exceeds 0.5 MPa, use PP honeycomb (6-8 mm cell), PET or PVC. Do not use MPP, XPS or PU.
- If skin thickness is below 1/15 of the cell size, use foam or a finer cell. Otherwise expect dimpling.
Hybrid cores often beat either one
Many of our vehicle programmes use both cores. A reefer floor with a honeycomb or CFRT structural deck over an MPP insulation layer gets pallet-jack capacity and FRC-level insulation in one laminate. An RV wall with an MPP field and solid PP strips at window and door frames gets insulation plus real screw-holding. Since both cores are polypropylene, they fusion-bond to PP skins without adhesive, and the hybrid stays 100% recyclable as a single polymer. That is not possible with a PU-plus-aluminium-honeycomb build.
Cost: Core Price Is Only Part of the Bill
Indicative 2026 prices for 20 mm core only, FOB China, per m². The PP honeycomb and MPP figures are our own; the others are market ranges for materials we do not manufacture.
| Core (20 mm) | Indicative core price (USD/m²) | Hidden costs to include |
|---|---|---|
| PP honeycomb | 6-14 | Edge closure on cut cells; inserts at hardpoints |
| MPP foam | 8-15 | Thicker section for the same stiffness |
| XPS | 2-4 | Needs thicker skins or a spreader layer to avoid wrinkling |
| PU (continuous or poured) | 3-6 | λ drift over 5-7 years; cannot be recycled |
| PET structural foam | 18-30 | Resin uptake on cut surface cells if infused |
| PVC structural foam | 30-50 | Price volatility; cannot be recycled |
| Aluminium honeycomb | 25-45 | Corrosion isolation; thermal bridging |
What the buyer actually pays for is the finished panel: core, plus skins, bonding, edge closure, inserts, scrap and freight. Our 2026 composite panel price guide breaks down finished panel FOB ($18-65/m² depending on build), MOQ tiers and 40HQ container loading. One point matters especially for cores: composite panels always fill a container by volume, not weight. A reefer wall with a 100 mm MPP core ships about 5x fewer m² per container than a 20 mm honeycomb wall, which is why we supply thick-core bodies as CKD kits.
Fire: Switching Cores Does Not Fix a Fire Rating
Buyers sometimes ask for "foam instead of honeycomb for better fire performance". PP honeycomb and MPP are the same polymer, with a heat of combustion around 44 MJ/kg, so changing the core geometry does not change the fire classification. Fire performance comes from flame-retardant grades, skins and test certification (FMVSS 302, ECE R118, EN 45545-2, ASTM E84). Our composite panel fire ratings guide explains which standard applies to which body.
Frequently Asked Questions
Is honeycomb core stronger than foam core?
In flatwise compression and shear at equal density, yes. PP honeycomb at 60-80 kg/m³ reaches 1.0-1.5 MPa in compression versus 0.4-0.9 MPa for micro-foamed PP of similar density, and 0.15-0.50 MPa for insulation foams like PU and XPS. High-density structural foams such as PET and PVC (80-150 kg/m³) match or exceed PP honeycomb, but they cost 3-5x more per m².
Which is better for insulation, honeycomb or foam core?
Foam, by a wide margin. PP honeycomb has an effective thermal conductivity of 0.06-0.08 W/m·K (about R-2.1 per inch), while closed-cell foams sit at 0.030-0.040 W/m·K (R-3.8 to R-4.8 per inch). To reach the ATP FRC refrigerated limit of U = 0.40 W/m²K, you would need about 175 mm of honeycomb versus 75-95 mm of foam.
Paper honeycomb vs PU foam core: which should I use?
Paper honeycomb is a low-cost core for doors, furniture and packaging used in dry, indoor conditions. It loses a large share of its compressive strength as humidity rises and fails permanently if it gets wet. PU foam insulates far better (0.022-0.032 W/m·K) and tolerates moisture, but it is weaker in compression. For vehicles, RVs or anything exposed to outdoor humidity, use neither: choose PP honeycomb for structure or a closed-cell foam (MPP, XPS) for insulation.
Can you combine honeycomb and foam in one sandwich panel?
Yes, and for reefer floors and RV walls it is often the best solution. Typical builds are a honeycomb or CFRT structural deck laminated over an MPP insulation layer, or an MPP wall with solid PP hardpoint strips at door and window frames. When both cores are polypropylene, they fusion-bond without adhesive and the panel remains recyclable as a single material.
Does a foam core make a sandwich panel fire rated?
No. Core geometry does not determine fire rating; polymer chemistry and certification do. PP honeycomb and MPP foam are both polypropylene and both burn unless flame-retardant grades are specified. Fire compliance has to be tested on the complete panel to the standard your market requires (FMVSS 302 for passenger compartments, EN 45545-2 for rail, ASTM E84 for buildings).
What is the MOQ for custom honeycomb or MPP panels?
Our standard MOQ is 200 m² for catalogue builds and 500 m² for custom cell sizes, densities or skin combinations. We send A4-size samples of both core types free on qualified enquiries, so you can compare them side by side before committing.
Related Guides
- Honeycomb Core Materials Comparison: PP vs Aluminum vs Nomex vs Paper
- Refrigerated Truck Body Panels: XPS vs PU vs MPP Insulation
- Sandwich Panel Construction: Core Materials, Skins & Bonding Methods
- Cutting, Joining & Fastening Composite Sandwich Panels
- RV Insulation Materials Compared: MPP vs Polyurethane vs XPS
- Composite Panel Price Guide 2026: FOB Cost, MOQ & Freight
Request Samples of Both Cores
The fastest way to decide is to hold both cores. Tell us the application (truck wall, reefer box, RV floor), panel thickness and yearly volume. We will send matched PP honeycomb and MPP samples with the same skins, plus a datasheet and FOB quote for each, within one working day.
Request a Quote for This Product | View PP Honeycomb Panels | View MPP Insulation Panels | Sandwich Composite Panels
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