By Suzy, Heart of Gold Sanctuary
Out here on the ranch, clothes take a beating. Mud, hay, sweat, cold mornings and hot afternoons, sometimes all in the same day. Over the years I've slowly swapped most of my polyester and fleece for wool, linen and organic cotton, and I've been asked a lot lately about the "fabric frequency" idea that's all over social media. So here's what I found when I dug into it, plus the real reasons I reach for natural fibers.
(That’s me on this post’s cover in a vintage silk dress. Silk is another natural fiber I love. It’s spun by silkworms, it’s light and breathable, and it doesn’t shed plastic in the wash.)
What is the "fabric frequency" claim?
You've probably seen the chart: linen and wool at 5,000, organic cotton at 100, conventional cotton at 70, and polyester, rayon and other synthetics at 15 or even zero. The idea is that natural fabrics carry a "higher frequency" that's good for your body, and plastic fabrics carry a low one that drags you down.
Those numbers trace back to a 2003 experiment by Dr. Heidi Yellen. She used a device called the Ag-Environ machine, which was built to measure a "signature" of agricultural products. The same readings are where the popular advice to never wear wool and linen together comes from (the combination supposedly read close to zero).
The honest part: those readings were never published in a scientific journal, the units aren't standard (they aren't hertz in the physics sense), and nobody has independently repeated them. So I don't treat the chart as science, and I won't sell you anything based on it. If the idea resonates with you, that's yours to decide, but you don't actually need it, because there are plenty of measurable reasons to choose wool and linen over plastic.
Polyester is plastic
Polyester, nylon, acrylic and spandex (also sold as elastane or Lycra) are all made from petroleum. That fleece jacket is basically a soft plastic bottle. That isn't automatically bad, since synthetics are cheap, stretchy and quick-drying, but it does come with some trade-offs.
1. Microplastics in every wash
Synthetic clothes shed tiny plastic fibers every time you wash them. One widely cited 2018 study in Environmental Pollution (De Falco and colleagues) estimated that a typical 5 kg load of polyester laundry can release over 6 million microfibers. Those go down the drain and into rivers, the ocean and farm soil. Wool, linen and cotton shed fibers too, but they're plant and animal fibers that break down instead of lingering for centuries.
2. Your skin is your largest organ, and sweat changes things
Your skin is a really good barrier, which is its whole job. Plastic fibers themselves are much too big to soak into healthy skin. What researchers are paying attention to now is the chemicals that can be in or on synthetic fabric, and whether those can move from clothing, through sweat, into your skin.
BPA in activewear: In 2022 and 2023 the Center for Environmental Health tested sports bras, athletic shirts and socks. It found BPA (a chemical linked to hormone disruption) in polyester-spandex blends from more than a dozen brands, some at many times California's Prop 65 safe-harbor level. So far its testing has only turned up BPA in polyester-spandex clothing. Its advice is to choose socks made mostly of cotton, wool or other natural fibers, and to change out of sweaty activewear soon after a workout.
Chemicals can travel in sweat: A 2024 University of Birmingham study in Environment International used lab-grown human skin models. It found that flame-retardant chemicals leaching out of microplastics into sweat could cross the skin barrier, and sweatier skin absorbed more. That was a lab study, not a study of people wearing clothes, and the researchers say the health effects still aren't fully understood.
"Forever chemicals" (PFAS): These are often used to make fabric stain-proof or waterproof. California now limits intentionally added PFAS in most clothing, which tells you regulators are taking the issue seriously.
Science on this is still young, and I'm not going to tell you your yoga pants are poisoning you. But the clothes that sit against your skin for hours, sweaty and warm (socks, underwear, sports bras, leggings, base layers, pajamas), are exactly where I've decided to go natural first.
One fair warning: natural doesn't automatically mean clean. Cotton can be treated with wrinkle-free finishes, and any fabric can be colored with harsh dyes. That's why I look for certifications (more on that below).
Why I love wool
It stays warm when it's damp. Wool can soak up a lot of moisture vapor and still feel warm, which matters on foggy Sonoma County mornings at feeding time.
It holds less odor. In a New Zealand study reported by Woolmark, trained smell testers found worn wool fabric held about 66% less body odor than polyester and about 28% less than cotton. I can wear wool socks and base layers more than once before washing, which also means fewer washes.
It handles temperature swings. Fine merino and alpaca are soft enough to wear right against your skin and work in both cool and mild weather.
It's naturally slow to catch fire compared to synthetics, which melt and stick. That's a nice thing to know if you're around wood stoves or campfires.
Why I love linen
It's made for heat. Linen comes from the flax plant. It's airy, it dries fast, and it feels cool on hot summer days.
It lasts. Linen is one of the strongest natural fibers, and it actually gets softer with every wash.
It's easy on the land. Flax generally needs less water and fewer pesticides than conventional cotton.
As for not mixing wool and linen? That one comes from old tradition, not from any testing I could find, so wear them however you like.
My favorite linen piece is this dress, hand dyed with natural plant dyes by my artist friend Zack Rhodes. It’s breathable, it’s one of a kind, and there isn’t a speck of plastic in it.
Me in a linen dress hand dyed with natural dyes by artist Zack Rhodes.
Quick comparison
Polyester, nylon, spandex: made from petroleum, sheds microplastics every wash, holds onto odor, lingers for centuries. Good for cheap stretch and quick drying.
Wool and alpaca: from sheep and alpacas, no microplastics, resists odor, biodegrades. Best for cold, damp weather and layering.
Linen: from the flax plant, no microplastics, breathable and fast-drying, biodegrades. Best for heat, summer and bedding.
How I shop for natural fibers
Read the tag, not the name. "Bamboo," "eco" and "recycled" can still mean rayon or polyester. Look for the percentages, ideally 100% or close to it.
Start with what touches your skin most. Socks, underwear, leggings, bras and sheets first, then outer layers.
Look for certifications. GOTS (Global Organic Textile Standard) covers organic fibers and processing. OEKO-TEX Standard 100 means the finished product was tested for a long list of harmful substances. For wool, the Responsible Wool Standard (RWS) covers how the animals and land are treated.
Buy fewer, better pieces. Good wool and linen cost more up front but outlast fast fashion by years. Vintage is another great way to get natural fibers for less.
If you keep some synthetics, wash them less, in cold water and full loads, and consider a microfiber-catching wash bag or filter.
Our favorite wool socks, leggings, alpaca pieces and linen finds will be linked right here as we add them to the shop. Every purchase through Tried and True helps feed the rescue horses at Heart of Gold Sanctuary.
This article is for general information and isn't medical advice. Some links on this site are affiliate links, which means we may earn a small commission at no extra cost to you. See our Affiliate Disclosure.
