Flotation foam works on a simple principle: a closed-cell foam is mostly gas trapped in sealed pockets, so it displaces more water than it weighs and floats. The engineering question is not whether it floats on day one — it is whether it still floats after a season in the water.
Why Closed-Cell Foam Floats
A foam's buoyancy comes from the volume of gas sealed inside it. In a closed-cell foam every cell is a sealed pocket, so the gas stays where it is and the material keeps its density. In an open-cell foam the cells are connected and water can displace the air — the foam gains weight, loses buoyancy and eventually sinks.
Density and Buoyancy
Buoyancy is the difference between the weight of water displaced and the weight of the foam itself. Because water is far denser than any of these foams, the reserve is large: the lower the foam density, the more buoyancy a given volume provides, but the softer and more compressible the foam becomes.
Bofeng Foam produces XPE and IXPE from 3x to 40x expansion, giving apparent densities from 26.8 to 300 kg/m³. The low-density end — the 25x to 40x range, roughly 26.8 to 40 kg/m³ — is where flotation boards and pool floats sit. Higher densities are used where the part also has to carry a structural load or hold a shape.
Water Absorption Is What Decides Long-Term Performance
| Property | XPE | IXPE |
|---|---|---|
| Expansion ratio | 3–40x | 3–40x |
| Apparent density (GB/T 6343) | 26.8–300 kg/m³ | 26.8–300 kg/m³ |
| Water absorption (GB/T 1034) | 0.4% or lower | 0.4% or lower |
| Chemical resistance | Water and moisture | Water, seawater, oils, acids and alkalis |
| Single-layer thickness | 3–15 mm | 0.1–15 mm |
| Laminated build | 15–200 mm | 15–200 mm |
A water absorption of 0.4% or lower is what keeps buoyancy stable. A material that took up several percent of its weight in water would lose a corresponding share of its reserve, and the loss would grow with every season in the water.
For salt water, IXPE is the better-specified grade: our factory data lists resistance to seawater, oils, acids and alkalis, and describes the material as antibacterial, non-toxic and odourless.
Building Thicker Flotation Parts
Single layers of XPE run 3 to 15 mm and IXPE from 0.1 to 15 mm. Thicker parts — flotation boards, thick cushions — are built by thermally bonding several layers, up to 200 mm in XPE and 100 mm in the functional grades. Foam can also be embossed for grip or laminated with a fabric facing.
Where the Material Stops
Bofeng Foam supplies foam as a buoyancy material. We do not manufacture, rate or certify finished lifejackets, personal flotation devices or other safety equipment.
Buoyancy rating, performance testing, certification and marking of a finished flotation device are the responsibility of the manufacturer of that device, under the rules of the market it is sold in. We supply the foam to the density, thickness and shape that device manufacturer specifies, and we make no claim about the performance of a finished device.
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Flotation Foam FAQ
What foam is used for flotation?
Closed-cell polyethylene foam — XPE for flotation boards and pool floats, IXPE where a thinner or denser layer is needed. The sealed cells trap gas, which is what produces buoyancy and keeps it stable in water.
Does flotation foam lose buoyancy over time?
Only if it takes on water. Our XPE and IXPE absorb 0.4% or lower by weight to GB/T 1034, so the reserve stays essentially unchanged in service. An open-cell foam would gain weight and lose buoyancy.
Can Bofeng Foam certify a lifejacket or flotation device?
No. We supply the foam as a buoyancy material only. Rating, testing, certification and marking of a finished flotation device belong to the device manufacturer.
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See also: Marine & outdoor foam hub · Is XPE foam waterproof? · All cross-linked foam materials · Contact Bofeng Foam