Merino vs Modal vs Cotton: Which Fabric Is Best for Underwear & Tees?

Three fibers dominate the luxury Italian basics category: merino wool (in EGI's wool-blend men's tees and MaRe's cotton-wool blends), modal (in EGI's women's slips and camisoles), and cotton (in TITTIMITTI® organic socks, Basic Cotton turtlenecks, and as the dominant fiber in MaRe's brushed-cotton fleece tees). Picking the right one for your wardrobe is not a matter of which is "best" in absolute terms — it's a matter of which set of trade-offs matches your climate, activity level, laundry tolerance, and skin sensitivity. This article walks through the measurable performance properties of each fiber per the published IWTO (International Wool Textile Organisation), Lenzing AG, and Cotton Incorporated standards, then closes with a practical decision tree for when to choose each.

The four properties that actually matter for base-layer fiber

When you strip away the marketing language, four measurable properties decide which fiber wins for any given garment:
Wicking rate — how fast the fiber moves moisture away from the skin (AATCC 195 vertical-wicking, mm/5min).
Thermal mass — how much heat the fiber absorbs and releases per gram (specific heat, J/g·K).
Odor-resistance — how quickly bacteria-driven odor develops in the worn garment (typically reported as wash-frequency-required, hours/days).
Care tolerance — what laundering the fiber survives without measurable degradation (ISO 5077 dimensional stability, ISO 6330 wash durability).
The fiber that wins on all four for every situation does not exist. Each fiber wins on two and loses on two. Match the wins to your use case.

Merino: the temperature regulator and odor champion

Merino wool is the temperature-regulator and odor-resistance champion. The natural crimp and air-trapping structure of merino fiber gives it a thermal mass roughly 2x that of cotton — meaning it warms slowly when cool and cools slowly when warm. The fiber's natural lanolin and surface chemistry inhibit the growth of odor-causing bacteria; merino t-shirts can typically be worn 3–5 times between washes without developing odor (per IWTO field studies). Merino's measurable downsides: it does not wick liquid water as fast as modal (the moisture-management is vapor-phase rather than liquid-phase), it can shrink under hot wash (always cold-wash), and it is more expensive per gram than cotton or modal. Use merino for: men's t-shirts, sleeveless muscle tanks, and short-sleeve undershirts in shoulder-season climates. The EGI Merino Wool Blend Men's Short-Sleeve Tee at TITTIMITTI® is the canonical example — 70% merino / 25% cotton / 5% elastane, IWTO-grade fiber at 18.5–19.5 micron.

Modal: the silk-feel, cotton-care moisture mover

Modal is the wicking and hand champion. Per AATCC 195, modal moves liquid moisture at approximately 95mm in 5 minutes — faster than every comparable base-layer fiber. The fiber also has a smoother surface than cotton (lower air-permeability index per ISO 9237) and a lower thermal mass — meaning it feels cool to the touch in warm conditions. Modal's measurable downsides: it has limited natural stretch (almost always blended with elastane for recovery), it has lower odor-resistance than merino (typical 1–2 wear cycles), and pure modal pills more readily than cotton on high-friction surfaces (the lace-trimmed slip is more pill-resistant than a plain modal t-shirt). Use modal for: women's slips, camisoles, lace-trimmed underwear, lounge tops, and any garment worn directly against skin under outer clothing. The EGI modal program at TITTIMITTI® — 92% modal / 8% elastane — is built for exactly this use.

Cotton: the universal default, with caveats

Cotton is the universal base-layer fiber because it is the most-tolerated by sensitive skin, the most widely-available across price points, and the easiest to care for. Combed cotton (longer-staple cotton from which short fibers have been removed before spinning) is significantly softer than carded cotton and is the standard for premium socks and underwear. Cotton's measurable downsides: it absorbs moisture into the fiber rather than wicking it away (a sweat-soaked cotton t-shirt stays heavy and cold), it has high thermal mass (slower to warm, slower to cool), and it shrinks more than modal or merino under hot wash. Use cotton for: socks, kidswear (the GOTS organic combed cotton in TITTIMITTI® is built for skin-contact safety), basic-rotation t-shirts, turtlenecks, and any garment where the skin-tolerance trade-off outweighs the moisture-management trade-off. The TITTIMITTI® house-line socks (100% combed cotton; 98/2 for kids') are this thesis applied.

Cotton-wool blends: the MaRe approach to year-round wear

MaRe's cotton-wool blend (70% cotton / 30% merino, brushed on the cotton face) is a classic Italian men's-undershirt construction that splits the difference between cotton's skin-tolerance and merino's temperature regulation. The brushed cotton sits next to skin (soft, well-tolerated, washable). The merino on the outside face manages temperature and moisture vapor. The blend at 180–200 gsm is heavy enough for shoulder-season layering, light enough to wear year-round in temperate climates. The MaRe Cotton-Wool Blend Men's Tank Top at TITTIMITTI® is the canonical example — the Italian canottiera classica, woven this way for over a century.

The decision tree: matching fiber to garment to use case

If you need to pick one fiber for one garment, the framework that consistently produces the right answer:
Slip, camisole, or lace-trimmed underwear, woman: modal blend (92/8 modal/elastane). EGI program.
T-shirt, short-sleeve, men's, daily wear: merino blend (70/25/5 merino/cotton/elastane) for shoulder-season; brushed-cotton-and-merino (70/30) for year-round; pure brushed cotton for warmer climates. EGI or MaRe.
Long-sleeve fleece tee, men's: 100% brushed cotton for winter base layer. MaRe.
Sleeveless muscle tank, men's: merino blend (50/50 merino/cotton) for cool-weather layering; pure cotton for warm-weather. MaRe or EGI.
Turtleneck, women's, year-round: 100% Italian cotton. Basic Cotton or Free Spirit.
Socks, daily wear, all genders, all ages: 100% combed cotton (98/2 for kids') with reinforced toe and heel. TITTIMITTI® house line.

Care: matching the laundry to the fiber

Each fiber has its own care optimum, all governed by the FTC Care Labeling Rule (16 CFR Part 423) and ISO 3758 international care symbols.
Modal: cold wash (≤30°C), mild detergent, no chlorine bleach, low tumble or air-dry. The 92/8 elastane blend tolerates a low-tumble dry but lasts longer air-dried.
Merino: cold wash with wool-rated detergent (Eucalan, Soak, or Woolite Delicates), no fabric softener, lay flat to dry. Do not tumble dry on heat — wool will shrink. The IWTO "Total Easy Care" merino can tolerate machine wash and tumble dry but always check the label.
Cotton (combed): warm or cold wash, any standard detergent, tumble dry low. Combed cotton tolerates significantly more abuse than modal or merino. GOTS-certified cotton requires the same care as any other combed cotton.
Cotton-wool blend: follow the wool care (cold, wool-detergent, low tumble), because the wool is the more sensitive component.

What the price tells you, by fiber

Honest mid-tier price ranges for each fiber, at the basic-construction level (no statement design, no embroidered branding):
Modal slip or camisole: $20–$50 retail honest; $200+ is brand-positioning markup.
Merino t-shirt: $30–$60 retail honest; $80–$120 retail for premium IWTO-grade fiber from a named mill.
Cotton-wool blend tank: $20–$35 retail honest.
Combed-cotton socks (3-pack): $20–$40 retail honest; $50+ for GOTS-certified organic combed cotton from named Italian mill.
Cotton turtleneck: $25–$50 retail honest.
The TITTIMITTI® catalogue prices ($10–$73) sit consistently in or below these honest ranges across all four fiber categories. The pricing is the result of buying direct from the Italian mill rather than through European wholesalers.

Sources and further reading

Primary sources: International Wool Textile Organisation (IWTO) Wool Fiber Standards; IWTO published research on wool-itch threshold (fiber diameter studies); Lenzing AG modal fiber technical sheets; Cotton Incorporated Cotton Yarn and Fabric Quality Guide; AATCC 195 (vertical wicking); ISO 5077 (dimensional stability after wash); ISO 9237 (air permeability); ISO 6330 (textile wash durability); FTC Care Labeling Rule (16 CFR Part 423); ISO 3758 (care symbols); Australian Wool Innovation publications on merino microns; Tilly's of Sydney merino-classification system; OEKO-TEX Standard 100 fiber testing; the IWTO "Total Easy Care" certification framework; published material from EGI and MaRe Italian mills (manufacturer specification sheets); Cotton Incorporated Lifestyle Monitor consumer surveys 2019–2024.