Filler bronze is judged on the fine end, and ours runs to 25 µm.
Makin and Pometon both publish bronze for PTFE compounding. The difference that matters in a seal compound is how fine the finest grade goes and how evenly it disperses.
These filler grades are in production use in PTFE bearings, bushings and seals, supplied as composition-controlled cuts under an ISO 9001:2015 system.
Side by side
| Attribute | Represented by UnstratBronze PTFE filler powders | Makin Metal Powders (UK) LtdZinc Bronze Powder and Irregular Bronze Powder124United Kingdom | Pometon S.p.A.Bronze CuSn10 Zn2 and CuSn range for resin and plastic fillers5Italy |
|---|---|---|---|
| Finest published cut145 | -500# (25 µm), on the CSPZ 45 grade | -350# on the zinc bronze datasheet (97% min below 45 µm); ultra-fine copper powders published separately at d(0.50) of 5, 10 and 20 microns | Range stated down to 45 microns |
| Size range for filler duty125 | -100# (150 µm), -200#, -325# and -500# (25 µm) | Zinc bronze published at -100# and -350#; irregular bronze at -100#, -300#, -350#, 100/350# and 60/240# | Wide particle size range stated across the bronze family; no cut list published |
| Composition145 | Zn 1.75 to 2.85%, Sn 8.5 to 9.5%, Cu balance on the main grades; CSPZ 45 at Sn 6 to 8%, Pb 2.5 to 3.5%, Zn 6 to 8%, Cu balance | Zinc bronze: Cu 88% min, Zn 1.5 to 2.5%, Sn balance; brochure grade CU88/Sn10/Zn2 | CuSn10 Zn2 named; percentages not published |
| Apparent density14 | Not published | 2.5 to 4.0 g/cc irregular zinc bronze, 1.0 to 3.0 g/cc dendritic; brochure irregular zinc bronze 3.3 plus or minus 0.3 g/cc at less than 45 µm | Not published |
| Morphology15 | Irregular | Irregular and dendritic morphologies both published for zinc bronze | Irregular, water atomised |
| Stated PTFE duty135 | Fillers in PTFE compounds for bearings, bushings and seals; improved wear resistance, thermal conductivity and load capacity over unfilled PTFE | Bronze filled PTFE for hydraulic seals named as a typical application on both the zinc bronze and irregular bronze sheets | Resin and plastic fillers named among bronze applications |
| Oxygen limit2 | Not published | 0.2% max on irregular bronze; not published on the zinc bronze sheet | Not published |
| Quality system4 | ISO 9001:2015 | ISO 9001 and ISO 14001 | Not published on the product page |
Competitor values are quoted from the vendor documents listed under Sources, as published on the date shown. Configurations vary, so treat every row as a starting point for the evaluation rather than a like-for-like test result.
What the table means
Dispersion is decided at the fine end
A bronze-filled PTFE seal fails at the agglomerate, not at the average particle. That is why the useful question is what the finest reliable cut is, and whether it is a bronze alloy or a copper powder. Our published range runs to -500# at 25 µm as a composition-controlled bronze. Makin's finest published zinc bronze is -350#, and its ultra-fine offering at d(0.50) of 5, 10 and 20 microns is published under copper rather than as an alloyed filler bronze.
What Makin publishes that we do not
Apparent density across four bands, a dendritic morphology option and an oxygen ceiling on the irregular bronze sheet. Dendritic particles interlock differently in a compound and some seal formulators want exactly that. Our sheet lists irregular only, and no apparent density. Both are worth asking about before a compounding trial.
Composition control across four cuts
The point of the range is that it is one composition family across a fourfold size span, so a compounder can shift cut without requalifying the chemistry. That matters when a seal grade moves from a coarse hydraulic application to a thin-wall bushing. The CSPZ 45 grade is the exception, a distinct chemistry for the finest work, and it is published as such rather than presented as the same material sieved harder.
Questions buyers ask
What is the best bronze filler for PTFE seals if I want an alternative to Makin?
If you need the finest dispersion, our -500# grade at 25 µm is finer than Makin's published -350# zinc bronze, and it is a composition-controlled bronze rather than a copper ultra-fine. Makin's advantages are published apparent density across four bands and a dendritic morphology option, which some seal formulators prefer for mechanical keying. Both firms name bronze-filled PTFE for hydraulic seals as intended duty, so this is a genuine like-for-like choice rather than a repositioning.
How much difference does bronze filler make to PTFE bearing performance?
Filled PTFE gains wear resistance, thermal conductivity and load capacity that unfilled PTFE cannot reach, which is why bronze-filled compounds dominate hydraulic seal and bushing work. The size distribution sets how evenly that improvement is spread through the part. Coarse filler in a thin-wall bushing gives you a wear surface with weak points, which is the reason the fine cuts exist.
Why buy filler bronze from a non-aligned supplier rather than a European one?
Seal and bushing production is unglamorous and easy to interrupt. If your hydraulics are made under a licence programme meant to reduce foreign dependency, sourcing the filler from a supplier inside another bloc's export regime keeps the dependency in place, one layer further down. The material is the same class; the exposure is not.
Do you publish apparent density for the PTFE filler grades?
No. Makin publishes 2.5 to 4.0 g/cc for irregular zinc bronze and 1.0 to 3.0 g/cc for dendritic. Ours is measured per batch and issued on request, and the missing published figure is logged as a gap rather than dressed up.
Sources
- 1. Makin Metal Powders (UK) Ltd, Product Data Sheet: Zinc Bronze Powder (copy held on this site)Retrieved: 2026-07-30 · Makin-branded product data sheet, published by its Swiss distributor Haeberlin & Co.
- 2. Makin Metal Powders (UK) Ltd, Product Data Sheet: Irregular Bronze Powder (copy held on this site)Retrieved: 2026-07-30 · Makin-branded product data sheet, published by its Swiss distributor Haeberlin & Co.
- 3. Makin Metal Powders (UK) Ltd, Irregular Bronze PowderRetrieved: 2026-07-30
- 4. Makin Metal Powders (UK) Ltd, Copper and Copper Alloy Powders (company brochure) (copy held on this site)Retrieved: 2026-07-30
- 5. Pometon S.p.A., Copper and copper alloyed powders, zinc and tin powdersRetrieved: 2026-07-30