Different Types of Fiber: A Fabric Buyer's Checklist (and What Viscose Shrinkage Taught Me)

I've been specifying performance textiles for outdoor brands for seven years. I've made fourteen mistakes that cost roughly $18,000 in reorders, failed wash tests, and wasted yardage. This is the checklist I now use before buying anything—fabric for a production run or yarn for a small project.

This checklist has seven parts. Use it if you're comparing different types of fiber, choosing a Polartec hoodie, evaluating a pair of Athleta Polartec leggings, or trying to decide whether a viscose garment will survive a washing machine. The steps are the same.

1. Different Types of Fiber: Don't Stop at Natural vs. Synthetic

Fiber content is the first filter, not the last. The big categories are animal fibers (wool, silk), plant fibers (cotton, linen), regenerated fibers (viscose, lyocell, modal), and synthetics (polyester, nylon, acrylic). Each category has a wide range of behaviors.

It's tempting to think synthetic equals sporty and natural equals delicate. But the actual performance depends on the yarn, the knit or weave, and the finishing. A nylon taffeta can feel crisp and tough. A polyester fleece can be soft and warm. A viscose knit can look expensive and then shrink into a child's top. The fiber type is real, but it's only one variable.

Fiber content tells you what the material is made of. It does not tell you how the fabric was constructed, how it was finished, or how it will behave after washing.

2. Brand Names Are Specifications, Not Magic

This is where Polartec comes in. Polartec hoodies are a good example of why a brand name doesn't replace a spec. Polartec makes many different fleece, stretch, and insulation fabrics: Thermal Pro, Power Stretch, Alpha, Power Dry, and others. A Polartec hoodie made from a midweight Power Stretch fleece behaves differently from one made from a lofted Thermal Pro knit. Both can be great. They're just not the same.

Same for Athleta Polartec leggings. Athleta has used Polartec stretch fabrics in leggings, and those garments rely on a different construction than a bulky hoodie. The inside may be brushed, the outer face may be smooth, and the elastane content affects how the fabric recovers. If you're ordering Polartec from a supplier, ask for the product family and the data sheet. If you're buying a garment secondhand, at least check the sewn-in fabric label.

The same idea applies to yarn. 'Wool' doesn't tell you whether it's lambswool, merino, or a wool blend. 'Acrylic' doesn't tell you whether it's soft or scratchy. The label is the beginning of the conversation, not the answer.

3. Does Viscose Shrink in Washing Machine? Yes—and the Label Usually Warns You

If your search history includes 'does viscose shrink in washing machine,' here's the direct answer: yes. It's not just possible; it's likely if the fabric is a loose knit and you use warm water or high agitation. Viscose is a regenerated cellulose fiber. It absorbs water and swells, and the swelling can change the fabric's structure as it dries. The result is lengthwise shrinkage, widthwise shrinkage, or both.

In 2022, I approved a viscose-blend hoodie sample without running a wash test. The lab's care label said machine wash cold, gentle. That was true. Also true: after one cold gentle wash and a flat dry, the garment had shrunk about 6% in length. It didn't look ruined hanging on a hanger. On a person, the sleeves were two inches too short. The order was $4,200. We sold it as irregulars at cost, and I wrote 'test everything' in permanent marker on the wall next to my desk.

One wash. Six percent.

Does that mean all viscose is bad? No. High quality viscose, properly finished, can be stable. Some viscose is blended with elastane or cotton to reduce shrinkage. Some is treated with resin finishes. But if the label says dry clean, don't gamble.

4. Places to Buy Yarn: Use the Same Label Checklist

What does yarn have to do with Polartec and viscose? More than you'd think. Whether you're buying yarn for a knitting project or choosing a knit fabric for a small line, the risk is the same: hidden fiber content, missing care data, and surprises after the first wash.

There are plenty of good places to buy yarn. Local specialty shops let you feel the skein and ask questions; online stores often have a bigger selection and detailed specs. Both are valid. The problem is when the label or listing is incomplete. I once ordered a 'worsted wool' yarn from an online shop that turned out to be 50% wool and 50% acrylic. It was fine for what I needed, but it didn't felt or block like wool. If I had made a sweater with it and washed it in a machine, the result would have been inconsistent.

Before you buy yarn from any source, get four things:

1. Fiber content by percentage—'wool' alone is not enough.
2. Yarn weight and suggested gauge—this affects the final fabric structure.
3. Washing and care symbols—especially whether it's hand-wash only or machine-safe.
4. Dye lot or lot number—if you need to match colors for a larger project.

5. The Step Most People Skip: Run a Wash Test Before You Commit

Here's the counterintuitive part. The most important step isn't reading the care label. It's testing the actual material. Labels are a starting point; they are not a guarantee. Different mills, dye lots, knits, and finishes can make the same fiber content behave completely differently.

When I say fiber content is the start, I do not mean it is unimportant. Fiber type sets the boundaries. Construction and finishing decide what you actually get.

For fabric orders, I ask for ISO 6330 wash test results. ISO 6330 is a standardized method for domestic washing and drying of textiles. It's not magic, but it gives me a consistent basis to compare one fabric against another. If a new supplier won't share wash test data, I treat that as a red flag. To be fair, some mills don't have the data because they haven't tested. That doesn't automatically make them bad. But it makes them risky.

For a one-off yarn purchase, you don't need ISO standards. Knit a swatch, wash it the way you plan to wash the finished item, and measure before and after. If the swatch shrinks more than you can tolerate, adjust the pattern or choose a different fiber. The cost of testing one swatch is tiny compared with the cost of remaking a sweater.

6. The $1,150 Lesson About 'Cheaper' Fabrics

In 2021, I saved $180 per bolt on a lookalike performance fleece. The mill was new, the price was good, and the hand feel was almost identical to the fabric I'd used before. Almost. Then our sample wash test showed pilling on the inside after two washes. The fabric was not acceptable for a hoodie. I reordered the correct fabric, lost a week of production, and paid $1,150 more for the fabric I should have ordered in the first place. The 'saving' was an illusion.

I get why cheap fabric is tempting. Budgets are real. But the hidden costs—reorders, delays, and lost credibility—are usually bigger than the upfront saving.

People think expensive fabric is a luxury. Usually it's an outcome. A fabric costs more when the mill has invested in testing, repeatable dyeing, and quality control. Paying for that is cheaper than paying for a failed order. To be fair, some lookalike fleeces are perfectly fine. There are good deals out there. But you can't identify them unless you ask for the same wash data you'd expect from a branded supplier.

7. What Changed in 2025—and What Didn't

The outdoor fabric world has changed a lot since I started in 2018. Recycled polyesters are standard now. Bio-based nylons and new fiber blends are everywhere. A 'performance fabric' from 2015 might look old-fashioned next to current stretch wovens with engineered moisture management. It would be silly to make decisions based only on old assumptions.

But the fundamentals haven't changed. Fiber composition, yarn construction, knit or weave structure, finish, and the care label still determine whether a fabric survives its first wash. The execution has transformed. The checklist is the same.

If you remember one thing from this checklist, make it this: fiber content is the start, not the answer. The label is the beginning of the conversation, not a guarantee. Everything else I learned cost money.