Does expanded polystyrene foam float?
Does expanded polystyrene foam float?
Yes
20 kg/m³ against water's 1,000
Expanded polystyrene foam floats. At 20 kg/m³ it is 50.00 times less dense than water, so about 2% of it sits below the surface and the rest above.
Why
Floating is decided by density alone — mass divided by volume — compared against the fluid. Weight has nothing to do with it directly: a 200-tonne ship floats and a 2-gram pebble sinks, because the ship encloses enough air to bring its average density below that of water. That is also the only reason a steel hull works.
The numbers
- Density
- 20 kg/m³ (11–35)
- Relative to fresh water
- 0.020×
- Floats in fresh water
- Yes
- Floats in seawater
- Yes
- Proportion submerged
- 2%
Compared with other materials
| Material | Density | Floats |
|---|---|---|
| air | 1.2 kg/m³ | Yes |
| expanded polystyrene foam ← | 20 kg/m³ | Yes |
| rigid polyurethane foam | 40 kg/m³ | Yes |
| EVA foam | 100 kg/m³ | Yes |
| balsa | 160 kg/m³ | Yes |
| corrugated cardboard | 160 kg/m³ | Yes |
| cork | 200 kg/m³ | Yes |
| western red cedar | 370 kg/m³ | Yes |
| spruce | 430 kg/m³ | Yes |
| pine | 500 kg/m³ | Yes |
Common questions
- Does expanded polystyrene foam float in water?
- Yes — at 20 kg/m³ it is less dense than water.
- Does weight decide whether something floats?
- No, density does. A 200-tonne ship floats and a small pebble sinks, because the ship encloses enough air to bring its average density below water.
Related pages
- Expanded polystyrene foam properties Density, melting point, strength
- Does air float? Yes
- Does rigid polyurethane foam float? Yes
- Does EVA foam float? Yes
- Does balsa float? Yes
- Does corrugated cardboard float? Yes
- Does cork float? Yes
- Does western red cedar float? Yes
- Does spruce float? Yes
Sources
- Typical range compiled from manufacturer specifications — At One Place