The yarn guide: cotton, bamboo, merino and recycled

Yarn decides how a sock feels, how long it lasts and what it costs. This is the practical version — what each yarn is actually good for, and where it is the wrong choice.

The short answer

Combed cotton is the volume standard: soft, strong, predictable, cost-effective.
Mercerized cotton buys lustre and colour depth for premium ranges, not durability.
Merino is for warmth and odour control; it costs several times more than cotton.
Bamboo and modal buy softness and drape — the right choice in comfort and underwear.
Recycled polyester (GRS) and organic cotton (GOTS) buy a claim your marketing can actually use.

Reviewed by the SOXMILL sourcing teamUpdated 8 October 2026Reading time: 6–8 minutes

Cotton: the default, and why

Combed cotton is the backbone of the sock industry because it does three things well at once: it feels soft, it is strong enough to survive repeated wear, and it takes dye predictably. "Combed" means the short fibres have been removed, which is what separates a soft sock from a scratchy one at the same nominal cotton content.

Mercerized cotton is treated under tension with caustic soda, which swells the fibre and produces a lasting lustre and deeper colour. It looks expensive and it photographs beautifully. What it does not do is make the sock more durable — for that you need reinforcement at the heel and toe, which is a construction decision, not a yarn one.

Choose combed cotton for: everyday, casual, sports, kids, work. Choose mercerized for: dress, business, gift ranges, premium menswear.

Organic cotton: same sock, verifiable supply chain

GOTS-certified organic cotton performs almost identically to conventional combed cotton. What you are buying is a verifiable supply chain with transaction certificates, so the claim on your packaging is defensible. If your brand makes an organic claim, that certificate is the difference between marketing and substantiation.

Expect a real cost premium. It is worth it if you are making the claim; it is money spent for nothing if you are not.

Bamboo and modal: softness and drape

Bamboo viscose is exceptionally soft, drapes well and has natural antibacterial properties. It is slightly less abrasion-resistant than cotton, which matters in workwear and matters much less in comfort socks and underwear. Modal is a modified viscose with excellent resistance to shrinkage and fading, and it takes colour beautifully.

Choose bamboo for: women’s comfort ranges, kids’, medical and diabetic socks, underwear. Choose modal for: premium basics, underwear, soft-touch fashion.

Merino wool: warmth without bulk

Merino regulates temperature, resists odour, and stays warm when damp — which is why it dominates hiking and thermal ranges. Fibre diameter matters: 19.5 micron is a reasonable mid-range, and finer fibres feel softer but cost more and wear faster.

Two practical points. Merino is several times the price of cotton, so it belongs in an outdoor or premium range rather than a value one. And it needs a nylon or polyester component for durability in the heel — a 100% merino sock in heavy use will wear through faster than a well-blended one.

Technical synthetics: polyamide and wicking polyester

Wicking yarns move moisture away from the skin and dry quickly, which is what makes them the right choice for running, cycling and any application where a wet sock causes blisters. Polyamide blends with elastane are the standard construction for graduated compression, because the pressure profile depends on elastic recovery being consistent and predictable, batch after batch.

Choose wicking synthetic for: performance sports, compression, travel, medical. In these categories it is not a cost compromise — it is technically the correct yarn.

Recycled polyester: a performance yarn with a claim attached

GRS-certified recycled polyester performs alongside virgin polyester and comes with a verified chain of custody, so the recycled-content claim on your packaging is substantiated. In performance socks it is often the strongest combination available: genuine technical performance plus a sustainability claim that stands up to scrutiny.

How to choose, in four questions

What is the wearing condition? Cold and damp → merino. Hot and sweaty → wicking synthetic. Everyday → combed cotton. Skin-sensitive → bamboo or modal.
What is your price point? Merino and certified yarns carry a real premium. If the price point cannot absorb it, choose a different yarn rather than compromising the spec silently.
Are you making a claim? Organic, recycled or responsible-wool claims need certified yarn. No claim, no need.
Where does the product fail first? Ninety per cent of the time it is the heel or the toe. Yarn choice matters less there than reinforcement — a construction decision.

Yarn comparison

Yarn	Good for	Weak at	Cost position
Combed cotton	Everyday, sports, kids, work	Moisture management	Baseline (lowest)
Mercerized cotton	Dress, business, gifting	Durability — it is a finish, not a fibre upgrade	Low–mid
GOTS organic cotton	Brands making an organic claim	Nothing performance-wise; it is a supply-chain claim	Mid (+ premium)
Bamboo viscose	Comfort, kids, medical, underwear	Abrasion resistance	Mid
Modal	Premium basics, underwear	Cost at high content	Mid
Merino wool	Hiking, thermal, outdoor	Cost; needs nylon for heel durability	High
Wicking polyamide	Sports, compression, travel	Natural hand-feel	Mid–high
GRS recycled polyester	Performance with a sustainability claim	Nothing performance-wise; certification adds cost	Mid
Acrylic blends	Volume winter, fleece-lined thermal	Pilling if poorly specified	Low

Frequently asked questions

Which certifications apply to your production?

OEKO-TEX® Standard 100, ISO 9001:2015, BSCI, SMETA 4-Pillar. Materials include GOTS organic cotton · RWS merino wool · GRS recycled polyester · bamboo, modal, combed and mercerized cotton · wicking polyamide blends. Certificates are shared on request, and third-party audits by SGS, Intertek or Bureau Veritas are welcome before shipment.

Which yarn is best for a first sock range?

Combed cotton for the volume styles and mercerized cotton for the dress or gift styles. That combination covers most price points without needing certified yarns, and it lets you add a bamboo or merino style later once you know which part of the range sells.

Is merino worth the cost?

In an outdoor or cold-climate range, yes — the warmth-to-weight ratio and odour resistance are genuinely better and customers notice. In a general range it usually is not, because the customer does not perceive the difference at the price point the product has to hit.

Do recycled yarns perform as well as virgin?

GRS recycled polyester performs alongside virgin polyester and carries a verified chain of custody, so the claim on your packaging is substantiated. It is one of the few places where the sustainable option is not a performance compromise.

How do I keep colour consistent between orders?

Yarn for a programme is allocated from a locked dye lot with the recipe held, colour is verified on a spectrophotometer at ±0.8 ΔE against a physical retained standard, and where volume needs more than one lot we produce a colour panel for approval before bulk. See materials and yarn for the full process.

How do you control quality?

One accountable QC chain from yarn to carton: yarn lot inspection on arrival, inline checks at knitting, linking, boarding and pairing, then AQL 2.5 final inspection with a photo report on every shipment. Our lab tests colourfastness (ISO 105), dimensional stability (±3% after five washes), pilling (ISO 12945-2) and mmHg pressure for compression styles.

Keep reading

Materials & yarn at the factory→ Sock size chart & gauge guide→ Cost breakdown guide→ Sports & athletic socks→ Thermal & outdoor socks→ Custom socks development→

Not sure which yarn fits your product?

Tell us the wearing condition and the price point — we will recommend one and explain the cost difference.

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