Wool vs. Acrylic: A Guide to Identifying Fibers

by Elizabeth / Tuesday, 11 October 2022 / Published in Textile Knowledge

Wool and acrylic are two of the most common fibers used in yarn production, each offering distinct properties that make them suitable for different projects. Knowing how to differentiate between them is crucial for choosing the right material for your needs. This guide provides a comprehensive overview of the key differences between wool and acrylic fibers.

1. Visual Inspection

While sometimes difficult for the untrained eye, there are visual cues that can help distinguish wool from acrylic.

Fiber Appearance

Wool: Typically has a more textured, crimped, or scaled appearance. The individual fibers often have a slightly fuzzy halo.
Acrylic: Tends to be smoother and more uniform in appearance. The fibers are often very straight and have a sheen or luster.

Yarn Structure

Wool: Can range from loosely spun to tightly spun, often exhibiting a more natural, less uniform twist.
Acrylic: Usually has a more consistent, even twist and a smoother surface.

2. Burn Test

The burn test is a reliable method for identifying fiber content. Exercise caution when performing this test, as it involves open flame.

How to Perform a Burn Test

Take a small sample of the yarn.
Hold it with tweezers or tongs.
Carefully expose it to a flame.
Observe how it burns, the smell of the smoke, and the residue left behind.

Burn Test Results

Feature	Wool	Acrylic
Flame	Burns slowly, may self-extinguish when the flame is removed.	Burns quickly and vigorously, continues to burn after the flame is removed.
Smoke	Smells like burning hair or feathers.	Has a chemical smell, sometimes described as acrid or plastic-like.
Residue	Forms a brittle, crushable ash.	Forms a hard, plastic-like bead.

3. Microscopic Examination

Microscopic examination provides the most definitive way to identify fibers.

Fiber Structure Under Microscope

Feature	Wool	Acrylic
Surface	Exhibits scales or overlapping cuticles, similar to human hair. These scales contribute to felting.	Has a smooth, even surface. Some acrylic fibers might have slight striations or a dog-bone cross-section.
Cross-section	Typically round or oval.	Can vary depending on the manufacturing process, but often round, dog-bone, or bean-shaped.

4. Other Physical Properties

Several other physical properties can help differentiate between wool and acrylic.

Elasticity and Resilience

Wool: Known for its excellent elasticity and resilience. It can stretch and return to its original shape, making it resistant to wrinkles and sagging.
Acrylic: Generally has good elasticity but not as high as wool. It can stretch but may not fully recover its original shape, leading to stretching or bagging over time.

Warmth and Insulation

Wool: Provides excellent warmth and insulation due to its crimped fibers, which trap air. It can also absorb moisture without feeling wet.
Acrylic: Offers good warmth but is not as insulating as wool. It is hydrophobic, meaning it repels water, but it doesn’t breathe as well as wool.

Care and Maintenance

Wool: Often requires hand washing or delicate machine washing. Can be prone to felting or shrinking if not cared for properly.
Acrylic: Typically machine washable and dryable, making it easier to care for. Resistant to moths and mildew.

5. Summary Table

Feature	Wool	Acrylic
Appearance	Textured, crimped, fuzzy.	Smooth, uniform, often shiny.
Burn Test	Smells like burning hair, brittle ash.	Chemical smell, hard plastic bead.
Microscopic View	Scales, round/oval cross-section.	Smooth, various cross-sections.
Elasticity	High.	Good, but less than wool.
Warmth	Excellent.	Good.
Care	Often requires delicate care.	Machine washable and dryable.