ULTEM 1000 or ULTEM 2300? Unfilled versus glass fibre

Few decisions on a drawing look smaller than ULTEM 1000 vs 2300, and few turn out to matter more. Both are PEI, both are amber, and both are stocked as sheet and rod, but one is tough and translucent while the other is stiff, opaque and dimensionally quiet. The choice changes stiffness, impact, machining and cost.

This guide sets the two grades side by side on the properties that decide real parts: stiffness, creep, thermal expansion, impact and notch sensitivity, and the practicalities of machining glass-filled PEI. It is aimed at design engineers who already know PEI is the right family and now have to pick a grade.

The two grades side by side

The simplest way to see the difference is to put ULTEM 1000 vs 2300 in the same column. ULTEM 1000 is the unfilled grade: amber and translucent, tough, and reasonably stiff for an unfilled polymer. ULTEM 2300 is the same PEI base with about 30 percent glass fibre, which makes it opaque, much stiffer and far more dimensionally stable, at the cost of impact strength and machinability.

Both share the PEI family strengths: high continuous service temperature, good flame behaviour and useful chemical resistance. Where they diverge is in modulus, expansion, impact and how they behave under a cutter. Both are stocked as sheet and rod across our stock shapes range.

Cost is the other difference. The glass-filled grade carries a premium, so it is chosen where its stiffness or stability does real work rather than as a default. Putting 2300 on a part that 1000 could carry simply spends money for nothing.

Stiffness, creep and thermal expansion

Glass fibre roughly triples the modulus. That matters most where a part must not deflect: a fixture, a jig or a structural bracket that would sag in unfilled PEI can hold its shape in 2300. The gain comes with a loss of the ductility that lets an unfilled part bend instead of cracking.

Thermal expansion falls just as sharply, from around 56 micrometres per metre per degree C for the unfilled grade to roughly 20 to 30 for the filled one. Over a long part and a wide temperature swing, that difference is the gap between holding a tolerance and losing it.

Creep tells the same story. A sustained load that would slowly deform 1000 will barely move 2300, so where a part carries load for years, the filled grade is usually the safer long-term choice.

Impact and notch sensitivity

Unfilled PEI is the tougher of the two and tolerates impact and abuse far better. The glass-filled grade is stiffer but more brittle: a sharp corner, a drilled hole or an over-tight fastener can start a crack, and glass-filled parts fail with less warning.

The answer is design discipline rather than a different polymer. Generous radii, no sharp internal corners, well-supported edges and controlled fastener torque let 2300 survive the duties it is chosen for. Where impact is the dominant load, 1000 remains the better pick.

A useful rule of thumb is to choose unfilled PEI wherever the part must survive a knock, and glass-filled PEI wherever it must not move. Rarely does one part need both, and where it does, a change of geometry usually solves the problem more cheaply than a change of grade.

Machining glass-filled PEI: tooling and edge quality

Glass fibre is abrasive. Tool life on 2300 is shorter than on 1000, edge chipping is more likely, and the finish is harder to control. Sharp carbide tooling, a positive rake and a light finishing pass keep the edge clean.

The unfilled grade machines much like other engineering plastics: freely, with a good surface and little edge damage. The filled grade rewards slower feeds and a more rigid setup, and it is worth reading our notes on milling glass-filled grades before quoting a tight edge.

Cooling and swarf clearance matter more than usual with an abrasive grade, because re-cutting glass-filled chips dulls the tool and spoils the edge. A steady air blast and a well-supported workpiece are usually enough to avoid it.

Transparency, colour and sterilisation

Transparency is a real selection criterion, not a cosmetic one. Unfilled PEI is amber and translucent, which lets a sight glass, a cover or a fluid path be inspected. The filled grade is opaque, so any application that relies on seeing through the part rules 2300 out at once.

Both grades are used in parts that must be cleaned and sterilised, and both take the routine methods used in medical and laboratory equipment. The unfilled grade keeps its translucency and shows soil clearly; the filled one hides it, which is not always an advantage on a hygiene line.

For a part that has to be seen through, the choice is made for you. For an opaque fixture, the filled grade’s stability usually decides it. Where both matter, the usual compromise is an unfilled part in a thicker section, if the weight and cost allow.

Questions buyers ask about ULTEM 1000 vs 2300

Is the glass-filled grade always better?

No. It is stiffer and more stable, but it is more brittle and harder to machine, and it costs more. It is the better buy only where stiffness or dimensional stability is the limiting requirement on the part.

Can I machine 2300 on the same setup as 1000?

Usually, with changes to tooling and feeds. The abrasive filler wears tools faster and chips edges more easily, so a fresh cutter, lighter finishing passes and a rigid workpiece are needed. The same programme can often run, but not at the same speeds.

Which grade suits a high-temperature fixture?

Glass-filled PEI is the usual choice for a fixture, because it resists creep and holds dimensions through thermal cycling. This is one of the common uses we see across the industries we supply, from semiconductor tooling to test rigs.

Does the glass filler change chemical resistance?

Broadly, the base resin sets the chemistry and the filler mainly changes mechanical behaviour. The filler can still affect surface wetting and how a part cleans, so it is worth testing a specific medium before committing. If a chemical is marginal, contact us with the medium, temperature and concentration.