For heat-resistant prototype parts in industrial equipment, the best specialty polymers are usually chosen based on temperature, mechanical load, chemical exposure, and how fast you need to prototype. Here are the top options, from most commonly used to more specialized:

1. PEEK (Polyether ether ketone)

• Best overall choice for high-temperature, high-performance prototype parts
• Continuous service temperature: ~250°C / 482°F
• Excellent:
  • Heat resistance
  • Chemical resistance
  • Mechanical strength
  • Wear and fatigue performance
• Good for:
  • Gears
  • Bearings
  • Valve parts
  • Electrical insulators
  • Structural prototypes in harsh environments
• Downsides:
  • Expensive
  • Harder to machine/print than standard plastics

2. PEKK (Polyether ketone ketone)

• Similar to PEEK, sometimes better for additive manufacturing
• Continuous service temperature: up to ~250°C
• Often:
  • More customizable processing
  • Slightly different crystallization behavior, which can help in 3D printing
• Good for:
  • Aerospace-like industrial prototypes
  • Tooling and functional test parts

3. Ultem / PEI (Polyetherimide)

• Very common for high-heat prototypes
• Continuous service temperature: ~170–200°C
• Excellent:
  • Dimensional stability
  • Flame resistance
  • Electrical properties
• Good for:
  • Housings
  • Brackets
  • Connectors
  • Thermal testing components
• Downsides:
  • More brittle than PEEK in some applications

4. PPS (Polyphenylene sulfide)

• Strong option for heat + chemical resistance
• Continuous service temperature: ~200–240°C
• Excellent:
  • Dimensional stability
  • Resistance to fuels, solvents, and many chemicals
• Good for:
  • Pump parts
  • Fluid handling components
  • Electrical and automotive industrial prototypes
• Downsides:
  • Can be more brittle than PEEK/PEI

5. PBI (Polybenzimidazole)

• One of the highest heat-resistant polymers available
• Continuous service temperature can exceed 300°C
• Extremely high:
  • Heat resistance
  • Wear resistance
  • Strength at elevated temperature
• Good for:
  • Very demanding industrial test parts
• Downsides:
  • Very expensive
  • Difficult to process
  • Less common for typical prototyping

6. High-temperature nylons (PA 6/6, PA 12, PA 46, PA 6T, PA 9T)

• Better when you need lower cost and decent heat resistance
• Especially PA 6T, PA 9T, PA 46
• Good for:
  • Functional prototypes
  • Snap fits
  • Brackets
  • Moderate heat environments
• Downsides:
  • Moisture absorption can affect dimensions and properties
  • Lower max temperature than PEEK/PEI/PPS

7. Glass- or carbon-fiber reinforced versions

• Often a better choice than the base resin if stiffness and dimensional stability matter
• Examples:
  • CF-PEEK
  • GF-PEI
  • CF-PPS
  • GF-PA
• Benefits:
  • Higher stiffness
  • Lower warping
  • Better load-bearing ability at temperature
• Downsides:
  • More abrasive to tools/nozzles
  • Can be more brittle depending on formulation

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Best choice by use case

• Highest performance overall: PEEK
• Best for 3D-printed high-temp prototypes: PEI (Ultem) or PEKK
• Best chemical + heat resistance: PPS
• Best extreme-temperature specialty polymer: PBI
• Best budget-friendly high-temp option: High-temperature nylon
• Best for stiffness and stability: Carbon-fiber reinforced grades

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Quick selection guide

Choose based on your conditions:

• Up to 120–150°C: high-temp nylon, PC blends, PPSU
• 150–200°C: PEI, PPS, some reinforced nylons
• 200–250°C: PEEK, PEKK, high-grade PPS
• Above 250°C: PBI or specialty composites

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Practical note for prototypes

If you’re making industrial prototype parts, the “best” material is often the one that:

1. Survives the target temperature
2. Holds tolerances under heat
3. Can be machined or 3D printed reliably
4. Is affordable enough for iteration

So in many real prototype jobs, PEI, PPS, and PEEK are the most practical starting points.

If you want, I can also give you:

• a comparison table of these polymers
• recommendations for 3D printing vs CNC machining
• the best polymer for a specific operating temperature or machine type