Most PUF panel brochures in India open with the same block of numbers: thermal conductivity 0.023 W/m·K, closed cells 92–95%, compressive strength 2.1 kg/cm², density 40 ± 2 kg/m³, "fire resistant". The block looks technical and reassuring. It is also nearly identical from one supplier to the next, because most of those figures describe rigid polyurethane foam as a material, not the panel you are buying.
We make PUF panels, and this article separates the two kinds of figure. The first kind is set by polyurethane chemistry and national standards and usually varies little between properly made foams. The second kind is set on the factory floor, varies from order to order, and is where buyers lose money. Our own specification for every product is on the live price board, line by line, and each line is explained in PUF panel specification.
Part 1: the properties that come from the chemistry
Rigid polyurethane (PUR) foam is a closed-cell plastic foam. At a density of 40 kg/m³, solid plastic makes up only about 5% of its volume; the rest is gas trapped in tiny closed cells. Almost every insulating property follows from that structure. The Indian standard for this material is IS 12436:1988, Preformed rigid polyurethane (PUR) and polyisocyanurate (PIR) foams for thermal insulation, with test methods in the IS 11239 series.
| Property | What the standard or the literature says | What it means for a buyer |
|---|---|---|
| Thermal conductivity (k-value, λ) | IS 12436: maximum 0.023 W/m·K at 10 °C mean temperature (Amendment 1, 2002), and 0.03 W/m·K at 50 °C. The European industry report adds an ageing allowance of about 0.005 W/m·K for pentane-blown foam under 80 mm thick. | Properly made PUR cores usually fall in a narrow band near this limit, but the exact figure depends on formulation, blowing agent, age and test temperature. A brochure quoting 0.023 is usually quoting the standard's limit; any other figure means little unless it states those conditions. |
| Closed-cell content | IS 12436: minimum 85%. Industry literature: above 90% is normal. | Closed cells are what make the foam rigid PU at all. "92–95%" separates no one. |
| Compressive strength at 10% deformation | IS 12436: minimum 115 kN/m² (Type 1) and 205 kN/m² (Type 2, for higher loads). | 2.1 kg/cm² is about 206 kN/m², which is simply the Type 2 minimum. Strength is mainly a function of density, so it is decided by the density you actually receive. |
| Dimensional stability | IS 12436: within ±2% after 24 hours at 100 °C. | A pass/fail property of the formulation. |
| Service temperature | IS 12436 rates PUR up to 110 °C and PIR up to 140 °C. European literature: long-term use about –30 °C to +90 °C. | Covers roofs, walls and cold rooms in India; very low-temperature cold storage uses thicker panels, not a different "grade" of k-value. |
| Water absorption | Literature: about 1.3% by volume after 28 days' immersion for a faced board; the effect on k-value is very small. | In a steel-faced panel the foam is sealed on both faces. Water problems come from joints, cut edges and site work, not from the foam's datasheet value. |
| Horizontal burning test | IS 12436: maximum 125 mm for PUR and 25 mm for PIR (IS 11239 Part 12). | A small laboratory strip test. Passing it is not a fire rating for a building (see Part 2). |
Two points that matter more than the table.
First, k-value ages. Fresh foam contains blowing-agent gas that insulates better than air. Over months and years some of it diffuses out and air diffuses in, and the conductivity rises; the guidance in IS 12436 itself notes that the value rises over time depending on conditions. Steel faces on both sides slow this exchange, which is one reason a sandwich panel holds its insulation value better than a loose board. Any k-value without a stated age ("initial" or "aged") and test temperature cannot be compared with another one.
Second, density changes strength far more than it changes k-value. Between about 30 and 100 kg/m³ the k-value barely moves, but compressive strength, panel stiffness and the bond between foam and steel all rise with density. So a low-density core can still "show" 0.023 on paper while being weaker in your roof. That is why density is one of the most useful checks on a core. It does not prove strength, uniformity or the bond to the steel, but a low figure is an early warning. More on this in PUF panel density.
Part 2: how to read the common PUF panel figures
Each figure below is often true, but quoted on its own it says less than it seems to.
1. The standard's limit, quoted as a test result. 0.023 W/m·K, 85–95% closed cells and 2.1 kg/cm² are the limits and typical values in IS 12436 and its sources. Printing them proves only that the seller has read the standard. Ask instead for the density of the core of your order and how it is checked.
2. A U-value with no thickness, or from a thicker panel. U-value is not a property of the foam; it is arithmetic on thickness. With k = 0.023 W/m·K and the usual surface resistances (about 0.17 m²K/W for a wall), a simple one-dimensional calculation gives the panel's U-value as roughly:
| Panel thickness | U-value (W/m²K), calculated |
|---|---|
| 30 mm | 0.68 |
| 40 mm | 0.52 |
| 50 mm | 0.43 |
| 60 mm | 0.36 |
| 80 mm | 0.27 |
| 100 mm | 0.22 |
These are illustrative figures for the panel alone, using wall surface resistances; in a real roof or wall, joints, fixings and thermal bridges change the result. On the same assumptions every 50 mm PUR panel calculates to about 0.43. A U-value is useful for choosing a thickness (see which PUF panel thickness to choose); it never separates two suppliers of the same thickness. If a quotation shows a U-value without the thickness beside it, ask which panel it belongs to.
3. "Fire resistant". Polyurethane is an organic, combustible material. "Fire resistant" in a brochure usually means the foam contains a flame-retardant additive and passes the small horizontal burning test above. That is not a fire-resistance rating of a wall or roof, which depends on the whole build-up, the joints and the fixings. IS 12436 itself says protection against external fire is necessary. If fire performance matters for your building, ask your designer what the building needs, and ask any supplier exactly what was tested, on what, and by whom.
4. Panel thickness measured over the crest. On a roof panel the steel has ribs (crests). A "100 mm" panel can mean 100 mm of foam, or 70 mm of foam plus a 30 mm crest. The insulation is the foam, so the thickness that matters is the thickness without the crest. Ask which one is quoted; we state ours as panel thickness without crest. See roof panel profile.
5. Sheet thickness: TCT or BMT, and a mill name instead of a specification. "0.5 mm sheet" can mean total coated thickness (TCT, steel plus metallic coating plus paint) or base metal thickness (BMT, steel only). The difference is real steel. Some sellers quote a well-known steel mill's name in place of a thickness and coating specification; the mill's name tells you nothing about which product of that mill was used. See sheet thickness.
6. Uni-coat or multi-coat. Many panels in the market are made on uni-coat sheets, a single paint layer, while the quotation shows only the steel mill and a colour. Multi-coat (primer plus top coat) and the dry film thickness (DFT) of the paint on each side decide how long the surface lasts. The price difference is small; the life difference is not. See coating.
7. Width and the area you pay for. Panels are billed per square metre, but per square metre of what? The cover (chargeable) width is the part that covers your building after the overlap. If a quotation prices on the overall width, you pay for steel that sits under the next panel. See panel width.
The lines to compare, and ours
Put two quotations side by side on these lines only. Each one is set by the factory, each one changes the panel, and each one can be checked on delivery.
| Line to compare | Why it matters | EasyPuf specification |
|---|---|---|
| Core density | Strength, stiffness, foam-to-steel bond | 40 kg/m³, rigid PUR |
| Panel thickness and how it is measured | Insulation is the foam only | Roof 30–100 mm, measured without crest; wall 40–100 mm; PUF slab 40–80 mm |
| Top and bottom sheet thickness (TCT) | Steel you actually receive | Roof: 0.5 / 0.3 mm or 0.3 / 0.3 mm nominal TCT; wall: 0.5 / 0.5 mm or 0.3 / 0.3 mm nominal TCT |
| Sheet type and standard | What the steel and metallic coating are | Galvalume AZ70 / PPGL, IS 15965 / ISO 16163 |
| Paint system and DFT, each side | Surface life | Multi-coat; top side RMP, primer plus top coat, 20 µ total DFT; back 10 µ total DFT |
| Cover (chargeable) width | The area you are billed for | Roof 1.00 m; wall 1.15 m (1150 mm ultra-wide panel) |
| Roof profile | Strength of the roof sheet, water run-off | Six-ridge with 30 mm crest |
| Length | Fewer joints, less waste | Cut to order |
Our full specification for each product, with today's factory price per sqm, is on the price board and on each product page. The same lines appear on every product, so they can be compared like for like.
How to check at delivery
- Density: cut a small block of core from an offcut, measure it, weigh it. Mass in kilograms divided by volume in cubic metres gives kg/m³. A 10 × 10 × 5 cm block of 40 kg/m³ foam weighs about 20 g.
- Sheet thickness: measure the steel at a cut edge with a micrometer, and remember the reading includes paint and metallic coating (TCT).
- Paint: a DFT gauge reads the paint film in microns on each side.
- Cover width: lay two panels, lock the joint, and measure from joint to joint.
- Thickness: measure the foam at a cut end, not over the crest.
Questions buyers ask
Is a lower k-value proof of a better PUF panel?
No. Properly made rigid PU cores usually fall in a narrow band in the low 0.02s, and IS 12436 caps it at 0.023 W/m·K at 10 °C. A difference in the third decimal, quoted without age and test temperature, tells you little about the panel in front of you. Compare density, sheet thickness, coating and cover width instead.
What U-value does a 50 mm PUF panel have?
About 0.43 W/m²K, using k = 0.023 W/m·K and normal surface resistances. On the same assumptions every 50 mm PUR panel calculates close to this figure, so U-value helps you choose a thickness but does not separate suppliers.
What density should the core of a PUF panel be?
For roof and wall panels, a core around 40 kg/m³ is normal; IS 12436 guidance places 37–80 kg/m³ with the higher-strength type. Our core is 40 kg/m³. What matters is that the density of your order is stated in writing and can be checked on an offcut.
Do PUF panels burn?
Yes. Polyurethane is combustible. "Fire resistant" usually refers to a flame-retardant additive and a small laboratory burning test, not to a fire rating of the building. For fire-critical buildings, ask your designer what the building needs, and ask any supplier exactly what was tested, on what, and by whom.
Why does the price differ when the brochures look the same?
Because the brochure figures are the same by nature, while density, sheet thickness, coating and width are not. Two panels with identical brochures can differ by several kilograms of steel per square metre and by years of surface life.
Where these figures come from
- The Part 1 figures are limits that IS 12436 sets for rigid PUR foam as a material.
- The U-values are calculations from the stated k-value and standard surface resistances, not measurements.
- The specification lines in the table above are what we manufacture to, and each one can be checked on delivery.
Sources
- IS 12436:1988, Preformed rigid polyurethane (PUR) and polyisocyanurate (PIR) foams for thermal insulation, Bureau of Indian Standards, with Amendment 1 (2002): text
- Thermal insulation materials made of rigid polyurethane foam, IVPU / PU Europe technical report: PDF
- U-values in this article are calculated from the stated k-value and standard surface resistances; they are not test results.