Merino
Fine-wool breed (Merino and crosses) selected for fiber diameter below 24 µm — the threshold that eliminates prickle sensation against skin. Combines natural temperature regulation, odour resistance, and moisture-vapor management in a single fiber. Softer than regular wool; less durable and more expensive than polyester.
Key Properties
| origin | merino_sheep |
| fiber class | natural_protein |
| max diameter um | 24 |
Decision Summary
Choose Merino when you need a natural fiber that performs next-to-skin: soft enough to wear against bare skin, warm enough for cold-weather base layers, moisture-managing enough to wear across activity levels, and odour-resistant enough for multi-day use. Merino is not a budget choice — it is the choice when natural fiber performance at the base layer is the requirement.
What Makes Merino Different from Regular Wool
Merino refers to a fine-fiber breed group selected for fiber diameter below 24 microns — the empirical threshold above which individual wool fibers generate a prickle sensation on skin [1]. Standard crossbred wool (25–40 µm) is coarser and is used in outerwear, carpets, and upholstery. Merino's fineness means every fiber that contacts skin exerts pressure over a smaller point, making the aggregate sensation smooth rather than prickly.
Beyond softness, Merino inherits all of wool's structural advantages: three-dimensional crimp for thermal insulation, a hygroscopic core that absorbs 14–18% of its weight in moisture vapor [2], and a scale surface that inhibits bacterial colonization responsible for odour. This combination produces a fiber that outperforms synthetic base-layer materials in temperature regulation across activity levels — at higher cost, greater care requirements, and lower abrasion resistance.
Merino Fiber Diameter Grades
| Grade | Diameter | Characteristics | Typical end use |
|---|
|-------|----------|----------------|----------------|
| Ultra Fine | <15.5 µm | Softest; rarest; most expensive | Luxury knitwear, baby garments |
|---|---|---|---|
| Superfine | 15.5–18.5 µm | Next-to-skin quality; soft for virtually all skin types | Premium base layers, fine knitwear |
| Fine | 18.5–22 µm | Comfortable next-to-skin for most people | General base layers, mid-layers |
| Medium | 22–24 µm | Perceptible to sensitive skin next-to-skin | Mid-layer outerwear knitwear, socks |
Super S Rating Guide
The Super S scale (Super 80s, Super 100s, Super 150s, etc.) is a commercial grading system that broadly correlates to fiber diameter. The approximate relationship:
| Super S Grade | Approximate fiber diameter |
|---|
|--------------|---------------------------|
| Super 80s | ~20 µm |
|---|---|
| Super 100s | ~18.5 µm |
| Super 120s | ~17.5 µm |
| Super 150s | ~16 µm |
| Super 200s | ~14–15 µm |
Super S is a useful guide but is not independently standardized across all markets. Reputable manufacturers back claims with IWTO-certified lab results [3].
Technical Profile vs Polyester (Base Layer Reference)
| Property | Merino Fine (18.5 µm) | Polyester | Advantage |
|---|
|----------|----------------------|-----------|----------|
| Moisture regain | 14–18% [2] | 0.4% | Merino (absorbs vapor; no wet-cling at low to moderate sweat levels) |
|---|---|---|---|
| Odour resistance | Excellent (multi-day wear) | Poor (bacteria colonize smooth surface) | Merino |
| Warmth when damp | Maintains ~80% [4] | Maintains ~95% | Polyester (marginally) |
| Drying time | 4–8 hours | 30–60 min | Polyester |
| Natural hand feel | Soft, natural | Smooth, synthetic | Merino |
| UV protection (UPF) | ~30–50 UPF [5] | Variable (construction-dependent) | Merino (inherent UPF) |
| Machine washability | Superwash-treated: yes | Yes | Comparable (treated Merino) |
Use-Case Matrix
| Application | Merino grade | Why Merino works |
|---|
|-------------|-------------|------------------|
| Base layer — cold-weather active | Superfine–Fine (15.5–22 µm) | Soft; moisture-wicking; odour-resistant across multi-day use |
|---|---|---|
| Travel shirt (multi-day, one shirt) | Fine (18.5–22 µm) | Odour resistance; machine washable (Superwash); wrinkle-resistant |
| Mid-layer knitwear | Fine–Medium (20–24 µm) | Warm, light; natural alternative to fleece |
| Running and trail socks | Fine–Medium with nylon reinforcement | Blister prevention; moisture management; odour control |
| Dress knitwear | Superfine (15.5–18.5 µm) | Professional appearance; comfortable under suit |
Sources and References
[1] Garnsworthy, R.K. et al., Understanding the Causes of Prickling and Itching Sensations in Human Skin, Wool Technology and Sheep Breeding. Prickle threshold study establishing ~22 µm diameter as critical boundary.
[2] Morton, W.E. & Hearle, J.W.S., Physical Properties of Textile Fibres, 4th ed. Woodhead Publishing. Moisture regain and fiber property data.
[3] International Wool Textile Organisation (IWTO), Wool Fiber Diameter Test Methods. IWTO-12 and IWTO-47 protocols.
[4] Holmér, I., Thermal Properties of Textile Fabrics. Wet insulation retention data for wool.
[5] Menzies, S.W. et al., UV Radiation Transmission Through Merino Wool Fabrics, Australian Journal of Wool Research. UPF measurement data.
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