Introduction: Density is the fastest way into a Rifeng WF datasheet, because it tracks how compressive, tensile, flexural, and shear values rise across 52WF, 75WF, and 110WF.
Composite workshops usually compare foam cores the same way: they line up the density grades first, then look at everything else. That habit exists for a good reason. Density tells you roughly how much polymer sits in each cubic meter of a closed-cell rigid PMI foam, and that single number shapes the compressive, tensile, flexural, and shear figures printed next to it. The three Rifeng WF grades — 52WF, 75WF, and 110WF — follow that pattern in a clean, readable way. The sections below cover what changes inside the foam as density climbs, what the typical values show across the three grades, and why sheet sizes and thickness ranges shift along with density.
How Density Shapes the Mechanical Role of a PMI Foam Core
PMI foam is a rigid closed-cell material. Its solid polymer forms cell walls and struts, and the gas sealed inside those cells adds almost no weight. When nominal density rises from 52 to 75 to 110 kg/m³, the number of cells does not change dramatically — the amount of polymer building each wall does. Thicker walls and struts resist bending and buckling better, so the foam reaches a higher stress before the cells collapse. That mechanism sits behind nearly every mechanical value in a WF datasheet, including the compressive strength measured under ISO 844 and the shear values measured under ASTM C273. It also explains why the three grades behave like points on one curve rather than three unrelated materials. In a sandwich panel, those values decide what the structural foam core actually does. The skins carry tension and compression while the core keeps them apart and transfers shear between them. A denser core transfers more shear at the same deflection, which is what the shear modulus column records. What stays constant across the three grades is the base polymer: every WF grade lists elongation at break of at least 2.5 percent under ASTM D638. So the difference between grades is not a different chemistry. It is how much of the same material is packed into each cubic meter, and that is why the strength numbers move together.
Reading the Property Trends Across 52WF, 75WF, and 110WF
The WF property values are typical values, published by the PMI foam manufacturer as reference figures for specification reading. Density itself is quoted as a range — 52 ± 12, 75 ± 15, and 110 ± 20 kg/m³ under ISO 845 — and that spread is normal for rigid foam. Keeping the tolerance band in view makes the rest of the numbers easier to compare.
1. Density Increase Raises Compressive and Shear Values Across the WF Grades
Compressive strength runs from 0.75 MPa at 52WF to 1.45 MPa at 75WF and 3.50 MPa at 110WF. Shear strength moves from 0.70 to 1.25 to 2.20 MPa, and shear modulus from 20 to 35 to 55 MPa. The step between 75WF and 110WF is larger than the step between 52WF and 75WF, which is common in rigid foam: once the cell walls are already fairly thick, adding more polymer pays off faster in collapse resistance. For a designer, that means the two lower grades cover moderately loaded panels, while 110WF is the grade that tends to appear when shear and compression dominate the load path and stiffness has to be bought with material rather than with thickness.
2. Tensile, Flexural, and Modulus Values Climb on the Same Curve
Tensile strength, measured under ASTM D638, rises from 1.65 MPa at 52WF to 2.45 MPa at 75WF and 3.50 MPa at 110WF. Flexural strength under ASTM D790 climbs from 1.55 to 2.40 to 4.60 MPa, and elastic modulus goes from 65 to 90 to 160 MPa. The gains move in the same direction but not at the same rate: flexural and modulus values widen their lead at the top grade, which reflects how much stiffer a thick-walled cell structure becomes once the walls carry load as a network rather than as thin membranes. Across all three grades, elongation at break stays at 2.5 percent or above, so the material is not becoming more brittle as it gets denser.
What Thickness and Sheet Size Differences Mean for Each Grade
Sheet geometry changes with the grade as well. Rifeng 52WF and 75WF are supplied as 2500 × 1250 mm sheets, while 110WF comes at 2300 × 1250 mm. Thickness ranges step down as density goes up: 1 to 120 mm for 52WF, 1 to 110 mm for 75WF, and 1 to 90 mm for 110WF. Thin stock from 1 to 4 mm is supplied as quarter or half sheets. Thickness tolerance is ±0.2 mm and length and width tolerance is ±2 mm across the series, which matters when cores are cut to fit a closed mold or stacked against a machined insert. Those numbers matter because panel thickness often influences bending stiffness more than density does. A 52WF core at 100 mm can beat a denser but thinner sheet in a bending panel, while 110WF at 30 mm suits a compact, highly loaded part where there is no room to grow the section. That is why density works as a first filter rather than a verdict: load direction, core thickness, resin uptake, and the curing process all shape the final choice, and no single WF grade fits every load case. The three grades are a ladder, and the useful question is which rung the panel actually needs.
Conclusion
Across 52WF, 75WF, and 110WF, density is the thread that ties the numbers together. The polymer chemistry stays the same and elongation at break stays at 2.5 percent or above, but more material per cubic meter produces steadily higher compressive, tensile, flexural, and shear values, along with a stiffer shear response. Sheet sizes and thickness ranges shift slightly between grades, while the ±0.2 mm thickness tolerance holds throughout. Reading the three grades as one continuous trend — rather than as three unrelated products — makes core specification faster. The Rifeng WF material reference lists the full typical values for all three grades if you want to line them up against a specific panel.
FAQ
Q：What is the density of Rifeng 52WF PMI foam?
A：Rifeng 52WF has a nominal density of 52 ± 12 kg/m³, measured under ISO 845. At that density the typical values are 0.75 MPa compressive strength, 1.65 MPa tensile strength, 1.55 MPa flexural strength, 0.70 MPa shear strength, and 20 MPa shear modulus. It is the lightest of the three WF grades and usually suits parts where weight control matters more than peak load.
Q：How do 75WF and 110WF PMI foam grades differ in compressive strength?
A：Compressive strength rises from 1.45 MPa at 75WF to 3.50 MPa at 110WF, both quoted as typical values under ISO 844, so the top grade is roughly 2.4 times stronger in compression. Behind that gap sits a density difference of 75 ± 15 versus 110 ± 20 kg/m³. Shear strength also roughly doubles, from 1.25 to 2.20 MPa, which is why 110WF appears in more heavily loaded panel designs.
Q：Does higher density always mean a better PMI foam core?
A：Not automatically. Higher density raises strength and modulus, but it also adds weight and material cost. A thicker lower-density core can deliver more bending stiffness than a thinner high-density sheet, and some projects care more about resin uptake, machining behavior, or the thickness range available at that grade. Density is a good starting point for comparing PMI foam grades, while the load case decides which grade wins.
Sources / References
ISO 9001 - Quality Management Systems | BSI
Lightweight Materials for Cars and Trucks | Department of Energy
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