​How to Identify PEI Plastic

What Is PEI Plastic?

Before learning how to identify it, it is important to understand what is PEI plastic.
PEI plastic, also known as Polyetherimide Plastic Material, is a high-performance engineering thermoplastic widely recognized for its excellent thermal resistance, mechanical strength, and inherent flame retardancy. One of the most well-known commercial forms of PEI plastic is ULTEM PEI plastic, which is commonly used in demanding industrial, electrical, medical, and aerospace applications.

Because PEI plastic material is often confused with other high-temperature plastics such as PC, PPS, or PEEK, proper identification is essential—especially when selecting materials for CNC machining, injection molding, or high-heat environments.

This article explains how to identify PEI plastic using visual inspection, physical properties, burning behavior, machining characteristics, and professional testing methods.

Understanding PEI Plastic Material

What Is PEI Plastic Made Of?

PEI Resin is an amorphous thermoplastic polymer composed of aromatic rings and imide linkages. This molecular structure gives PEI material its outstanding heat resistance, rigidity, and dimensional stability.

Key characteristics of PEI plastics include:

• Continuous service temperature up to 170–180°C

• Glass transition temperature around 217°C

• Inherent flame retardancy (UL94 V-0, without additives)

• High strength and stiffness

• Excellent electrical insulation

• Good chemical resistance

Because of these properties, PEI plastic material is often supplied in the form of PEI plastic sheet, rods, tubes, and precision-molded components.

Visual Identification of PEI Plastic

Color and Transparency

One of the easiest ways to identify PEI plastic is by its appearance:

• Typically amber, translucent brown, or yellowish

• Semi-transparent rather than fully clear

• Some grades may appear black when combined with High Temperature Black Masterbatch, but still retain PEI’s inherent rigidity

Tip: If you see a hard, amber-colored engineering plastic sheet, there is a strong chance it is a PEI plastic sheet.

Physical Property Identification

Hardness and Rigidity

PEI material is noticeably rigid and stiff:

• Difficult to bend by hand

• Resistant to surface scratching

• Feels harder than ABS or nylon

Heat Resistance Test

When gently heated (for example, with controlled hot air):

• PEI plastic resists softening

• Maintains shape far longer than PC or ABS

• Does not melt easily under moderate heat

This excellent thermal behavior is a defining feature of Polyetherimide Plastic Material.

Burning Characteristics (Controlled Environment)

Burn testing should only be conducted by trained professionals.

When tested, PEI plastics show distinctive behavior:

• Difficult to ignite

• Self-extinguishing when flame is removed

• Produces minimal smoke

• Leaves a dark, rigid residue

These flame-retardant properties come directly from the molecular structure of PEI resin, not from added flame retardants.

Machining Characteristics of PEI Plastic

For engineers familiar with CNC operations, machining behavior can help identify PEI plastic material.

During CNC milling or turning:

• Chips are short and brittle

• No melting or stringing

• Excellent dimensional stability

• Clean surface finish after machining

Because of these traits, ULTEM PEI plastic is frequently chosen for high-precision CNC components, fixtures, and electrical insulation parts.

Professional Identification Methods

For absolute confirmation, laboratory testing is recommended.

FTIR Analysis

• Identifies chemical structure

• Confirms PEI resin composition

DSC (Differential Scanning Calorimetry)

• Detects glass transition temperature (~217°C)

• Distinguishes PEI material from PC or PPS

Material Documentation

• Look for datasheets or certificates listing:

• Polyetherimide

• PEI plastic

• ULTEM PEI plastic

• PEl Plastic Material / PEl Resin

Differentiating PEI from Similar Plastics

Understanding these differences helps avoid costly material selection errors.

Common Applications of PEI Plastics

Due to its superior performance, PEI plastic material is widely used in:

• Electrical and electronic insulation components

• Aerospace interior parts

• Medical device housings

• Semiconductor equipment

• Automotive high-temperature fixtures

• CNC-machined structural parts

In many of these applications, PEI plastic sheet and rods are preferred due to their machinability and stability.

How to Identify PEI Plastic

To correctly identify PEI plastics, focus on the following key indicators:

1. Amber or translucent brown appearance

2. High rigidity and surface hardness

3. Exceptional heat resistance

4. Self-extinguishing flame behavior

5. Stable CNC machining performance

6. Laboratory confirmation via FTIR or DSC

By understanding what is PEI plastic and recognizing its defining features, engineers and manufacturers can confidently select Polyetherimide Plastic Material for high-performance and high-temperature applications.