Two of the most capable engineering thermoplastics on the market, priced and performing worlds apart. Here's how to tell which one your application actually needs — before it costs you.
If you've spec'd a high-performance plastic before, you've probably had this conversation: "Do we really need PEEK, or will Ultem do the job for less?" It's one of the most common questions we field at Emco, and the honest answer is — it depends on what's actually failing in your application. Below, we break the decision down across the four factors that matter most: cost, machinability, temperature range, and chemical resistance.
This is usually the first question, and for good reason — PEEK typically runs two to three times the price of Ultem 1000 in comparable stock shapes. On a small bracket, that difference might not move your budget. On a run of machined components, it can be the difference between a project that pencils out and one that doesn't.
The catch: PEEK's higher cost buys real performance headroom. If your application only needs what Ultem already delivers, PEEK is money spent on capability you'll never use. If it needs what PEEK delivers, Ultem is a false economy — you'll pay for it in field failures instead of on the purchase order.
Ultem 1000 machines cleanly, holds tight tolerances, and produces good surface finish without excessive tool wear — one reason it's a favorite for prototyping and short-run precision parts. PEEK is also machinable and performs well in production, but its semi-crystalline structure and toughness generate more heat at the tool interface and wear tooling faster, especially in deep or high-speed cuts. Neither material is difficult to work with in an experienced shop, but if your part geometry is complex and your timeline is tight, Ultem's forgiving nature can shorten cycle time.
This is where the two materials diverge most sharply. Ultem 1000 holds up well to roughly 340°F in continuous service, with a heat deflection temperature high enough for most demanding mechanical applications. PEEK pushes that ceiling to around 480°F, and unlike many plastics, it keeps meaningful strength and stiffness as it approaches that limit rather than going soft early.
If your part sits near a heat source, cycles through sterilization ovens, or operates in continuous high-temp service above roughly 350–400°F, Ultem is likely to be working near its limit. PEEK is the safer choice for sustained exposure in that upper range.
Ultem 1000 handles many common industrial fluids well, but it's vulnerable to certain solvents, some fuels, and prolonged exposure to high-pH cleaning chemicals — and it can be sensitive to hydrolysis under repeated steam or hot-water exposure over time.
PEEK is in a different class here. It resists nearly the full range of industrial chemicals, holds up to repeated autoclaving and steam-in-place cycles, and is the standard choice for semiconductor process equipment and medical devices that face aggressive sterilization schedules. If your part will see repeated chemical washdown, superheated steam, or aggressive solvent contact, PEEK's chemical resistance alone may justify the price difference.
| Factor | Ultem® 1000 Wins When... | PEEK Wins When... |
|---|---|---|
| Budget | Cost is a primary constraint | Performance justifies premium |
| Temperature | Service temp stays under ~340°F | Service temp exceeds ~350–450°F |
| Chemical exposure | Exposure is mild/occasional | Repeated steam, solvents, or autoclaving |
| Machining | Complex geometry, tight timeline | High-volume production runs |
| Flame rating | Inherent V-0 rating needed, no additives | Comparable via specific PEEK grades |
| Fatigue/wear life | Moderate cyclic loading | High-cycle fatigue, bearing/wear apps |
Most applications we quote don't actually need PEEK — but a meaningful minority absolutely do, and using Ultem there is the more expensive mistake in the long run. If you're not sure which side of that line your application falls on, send us the operating conditions (temperature, chemical exposure, load, and duty cycle) and we'll help you land on the right call before you commit to material.
Talk to Emco's team — we'll help you match the material to the application, not the other way around.
