The Short Answer
Solid PTFE sinks. At 2.14–2.20 g/cm³ it is roughly twice the density of water. If your application needs a floating sphere, you need either a hollow PTFE ball or a lighter polymer — and the choice between those two comes down to whether you actually need PTFE's chemistry.
The Three Options
1. Polypropylene — the default
PP has a density around 0.90 g/cm³, so it floats naturally with no special construction. It handles most aqueous chemistry, acids, alkalis and salt solutions well up to about 100°C, and it is the cheapest option by a wide margin. For tank level floats, sight glasses, float switches and water treatment duty, PP is usually the correct answer and specifying anything else is overspending.
Its limits: it softens near 100°C, embrittles below about 0°C, and is attacked by strong oxidisers and aromatic or chlorinated solvents.
2. UHMWPE — buoyant and tough
At roughly 0.93–0.94 g/cm³, UHMWPE also floats, and it brings outstanding abrasion resistance and near-unbreakable impact strength. It handles a similar chemical range to PP with better mechanical durability. Its ceiling is about 80°C — lower than PP — so it is the choice where the float sees mechanical knocking or abrasive media rather than heat.
3. Hollow PTFE — buoyancy with full chemical resistance
A hollow PTFE ball is made by machining two hemispheres and joining them with thermal fusion and chemical welding. The enclosed air makes the assembly buoyant while every wetted surface remains PTFE.
This is the answer when the float has to survive conditions PP and UHMWPE cannot: hot acid, strong oxidisers, chlorinated solvents, or service above 100°C. It costs considerably more than either alternative because it involves machining two parts and a welding operation rather than molding one.
How to Choose
| Condition | Use |
|---|---|
| Water, mild chemistry, under 100°C | Polypropylene |
| Abrasive or impact-prone, under 80°C | UHMWPE |
| Aggressive chemistry or above 100°C | Hollow PTFE |
| Strong oxidisers, chlorinated solvents | Hollow PTFE |
| Needs to sink, not float | Solid PTFE |
Practical Notes on Hollow PTFE
- Weld integrity is everything. If the joint leaks, the ball fills and stops floating. This is the failure mode to ask about — and the reason to buy from someone who makes them rather than resells them.
- Pressure limits apply. A hollow sphere under external pressure can collapse. State the operating pressure at the enquiry stage; it affects the required wall thickness.
- Temperature affects buoyancy. The enclosed air expands with heat, so a hollow ball under a large temperature swing is not a constant-buoyancy device.
- Specify the buoyancy you need, not just the diameter. Wall thickness determines how much of the sphere sits above the liquid line.
A Common Mistake
Specifying solid PTFE for a float because "PTFE is the chemically resistant one," then discovering on commissioning that the float sits on the tank bottom. If chemical resistance is what drove you to PTFE and buoyancy is what the application needs, hollow PTFE is the only construction that gives you both.