Why Modal Is Not a Natural Fiber

If Viscose is the "first generation" of rayon, Modal is the high-performance "second generation." Developed to address the primary weakness of standard rayon—its tendency to lose strength and shrink when wet—Modal was engineered with a modified molecular structure. It occupies a specific niche in the textile industry: it offers the botanical origin of a natural fiber with the engineered durability of a synthetic.

1. Modal Technical Classification: The "High Wet Modulus" Distinction

In the textile industry, Modal is defined not just by what it is made of, but by how it behaves when wet. The ISO 2076 standard, which regulates generic fiber names globally, gives Modal its own classification code (CMD) separate from standard Viscose (CV) [Source 204].

The defining trait of Modal is High Wet Modulus (HWM).

• The Problem with Standard Viscose: Regular rayon has "low wet modulus," meaning it becomes weak and stretchy when wet. It can lose up to 50% of its strength in the wash, leading to shrinking and warping [Source 541].
• The Modal Solution: Modal fibers are engineered to possess high breaking strength and high wet modulus. This means the fiber retains its structural integrity even when saturated with water, making it machine washable and tumble-dry safe [Source 204, 542].

2. Modal Manufacturing: How Beechwood Becomes Fabric

Modal is almost exclusively derived from Beech trees (Fagus sylvatica). The manufacturing process is a modified version of the viscose method, optimized for higher crystallinity.

1. Pulping: Beechwood chips are digested to extract pure cellulose. Beech is preferred because it is a self-propagating tree that requires no artificial irrigation [Source 852].
2. Xanthation: Similar to viscose, the pulp is treated with caustic soda and carbon disulfide to create a liquid solution.
3. Modified Spinning (The Key Difference): Unlike standard viscose, Modal is spun into a chemical bath containing zinc sulfate. Crucially, the fibers are stretched (drawn) significantly during this solidification process [Source 542].

Why Stretching Matters: Stretching the fiber while it forms aligns the internal cellulose molecules in parallel. This increased "molecular orientation" is what gives Modal its superior strength compared to the random, amorphous structure of standard viscose [Source 551].

3. Modal vs. Viscose: A Durability Comparison

While both fibers belong to the "Rayon" genus, they are distinct species with different performance metrics. Sourcing experts and technical manuals distinguish them as follows:

4. References

1. ISO 2076:2021 Textiles — Man-made fibres — Generic names. International Organization for Standardization.
2. Federal Trade Commission. "Bamboo Textiles." Business Guidance.
3. Lenzing AG. "VEOCEL™ Viscose – Created With Care, For The Environment."
4. Szoneier Fabrics. "Rayon vs Viscose Fabric: Key Differences Explained."
5. Eleutério, T., et al. "A Review of Natural Fibers: Classification, Composition, Extraction, Treatments, and Applications." Fibers 2025.
6. Sport Casuals International. "What Are Viscose, Modal, and Lyocell Fibers?"
7. Robert Owen. "Viscose vs. Modal vs. Lyocell - Difference?" Apr 2017.

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FINAL WORD: Modal is not a natural fiber, so you won't find it at ShirtCastle.