After our 30-day user study on skin, hair, and sleep, we wanted the fabric physics behind those results measured independently. Not as a feeling. As lab data. Below are the key findings from The Moonchild Silk Pillowcase Lab Study 2026.
In this article
Study Design
- Laboratory: CTL® GmbH, Chemisch-Technologisches Laboratorium, Bielefeld
- Accreditation: DAkkS D-PL-11062-01-00
- Scope: GOTS Standard Version 7 plus CTL guidelines
- Our silk: 100% silk, GOTS-dyed
- Comparison: 100% cotton, grey
- Also tested: 100% linen, GOTS-certified, botanically dyed
Tests covered friction, rubbing and washing fastness, absorbency (wicking), evaporation, water-vapour and air permeability, pH, and harmful substances (azo dyes / MAK amines, aniline, formaldehyde, APEOs, heavy metals).
Key Lab Findings
- Silk reduces friction by up to 24% compared with cotton.
- Our GOTS dye holds at grade 5 — the highest grade on the grey scale. No visible fading of the silk in the wash test.
- Banned azo dyes, formaldehyde, and APEOs: not detectable.
- Silk wicks moisture about 70% higher than cotton and evaporates it faster.
- Breathability is 2.7× the specified laboratory value. Water vapour permeability: 5474 g/m²/24h — 174% above the minimum of 2000.
Laboratory overall assessment: requirements fulfilled.
1. Friction: why silk is gentler on skin and hair
Friction is the physical reason cotton pillowcases rough up hair and press sleep creases into skin. The laboratory compared silk and cotton with the same CTL method.
| Measurement | Moonchild silk | Cotton | Difference |
|---|---|---|---|
| Frictional resistance | 0.353 N | 0.462 N | −24% |
| Coefficient of friction μ | 0.58 | 0.75 | −23% |
Silk reduces friction by up to 24% compared with cotton.
Frictional resistance is the force in newtons needed to make the fabric slide. The coefficient of friction is the same measurement, independent of how hard the fabric is pressed. Both numbers say the same thing: silk’s fine, smooth surface creates less resistance.
Due to the fine, smooth surface of silk, the frictional resistance is lower than with cotton.
This is the lab basis for less frizz, fewer split ends, and fewer sleep creases — the same effects our 30-day user study confirmed for 94% of testers on unruly hair and 89% on fine lines.
2. Moisture: wick, breathe, dry
Night sweat and skincare sit longer on cotton. We had the lab measure whether silk takes moisture up better and releases it faster.
Absorbency (wicking, 5 minutes)
Laboratory benchmark: more than 50 mm rise in 5 minutes.
| Fabric | Lengthwise | Widthwise | Benchmark |
|---|---|---|---|
| Moonchild silk | 68 mm | 68 mm | met |
| Cotton | 38 mm | 42 mm | below |
| Moonchild linen | 27 mm | 25 mm | below |
Silk wicks moisture about 70% higher than cotton. The fabric takes up sweat and moisture instead of leaving them trapped between skin and pillow.
Evaporation after 30 minutes
Benchmark: at least 17% of the applied moisture evaporated after 30 minutes.
| Time | Silk | Cotton | Linen |
|---|---|---|---|
| 5 minutes | 4.75% | 4.64% | 4.64% |
| 15 minutes | 11.26% | 8.28% | 8.28% |
| 30 minutes | 20.02% | 15.91% | 26.76% |
| Benchmark ≥ 17% | met | below | met |
Silk evaporates body moisture faster than cotton. After 30 minutes it sits above the laboratory benchmark; cotton sits below it. In the first 15 minutes, silk is clearly ahead.
Linen evaporates the most after half an hour, but wicks the least. For a pillowcase — skin and hair on the fabric all night — the combination that matters is high uptake plus fast release. That combination belongs to silk.
Breathability
| Measurement | Silk | Cotton | Lab benchmark |
|---|---|---|---|
| Water vapour permeability | 5474 g/m²/24h | 4890 g/m²/24h | ≥ 2000 |
| Air permeability | 332 l/dm²/min | 490 l/dm²/min | > 80 |
Both fabrics breathe well above the benchmark. Silk lets water vapour through at 5474 g/m²/24h — 2.7 times the specified minimum of 2000, or 174% above the laboratory requirement. Cotton is more air-permeable (a more open weave). For sleep climate, vapour transmission is what counts: moisture should leave the skin, not just air moving through the cloth.
3. GOTS dye: color holds at grade 5
Our silk is GOTS-dyed — certified, screened for harmful substances, approved for skin contact. The question was: does this sustainable dye hold in everyday use?
Important: this section is only about our silk. The laboratory did not rank the comparison cotton’s color against the silk. It measured whether the silk color itself faded — and whether it transferred onto other fabrics in the wash.
Colourfastness is graded on a grey scale. Grade 5 is the best rating, grade 1 the worst.
Does the silk itself stay colour-stable?
| Test on the silk | Requirement | Silk result |
|---|---|---|
| Rubbing fastness, dry | minimum 3 | 5 |
| Rubbing fastness, wet | minimum 2 | 5 |
| Washing fastness: change of colour of the silk | minimum 3–4 | 5 |
Our sustainable dye holds at grade 5. The silk itself shows no visible fading in the wash test. No colour rubs off dry or wet.
Does the silk bleed onto other fabrics in the wash?
In the wash test, a standard multifibre strip lies against the silk. The laboratory checks whether rose dye transfers onto those other fibres. The higher the grade, the less staining.
| Does silk dye transfer onto … | Requirement | Grade |
|---|---|---|
| Wool | minimum 3–4 | 5 |
| Acrylic | minimum 3–4 | 5 |
| Polyester | minimum 3–4 | 5 |
| Polyamide (nylon) | minimum 3–4 | 5 |
| Acetate | minimum 3–4 | 5 |
| Cotton adjacent strip | minimum 3–4 | 4–5 |
On five of six adjacent fibres, the silk scores a perfect 5 — no staining. Only the cotton adjacent strip is 4–5 — still above the requirement, and practically no visible staining. That is a slight tendency, not bleeding.
In short: the GOTS colour stays on the silk. It does not transfer onto skin, hair, or the rest of the wash.
Note: the silk was tested with a hand-wash procedure — the method that belongs with silk. Lightfastness (sun fading at a window) was not part of this commission.
4. Harmful substances: what sits on your skin
A pillowcase rests against face and hairline for eight hours. Chemical testing was therefore required, not optional.
| Parameter | Limit | Moonchild silk |
|---|---|---|
| MAK amines / azo dyes | < 20 mg/kg | not detectable |
| Aniline from azo dyes | < 100 mg/kg | not detectable |
| Formaldehyde | qualitative | not detectable |
| APEOs (NP/OP ethoxylates) | < 20 mg/kg | not detectable |
| pH of aqueous extract | 4.0–7.5 | 6.7 |
| Nickel, extractable | < 1 mg/kg | not detectable |
| Zinc, extractable | < 750 mg/kg | not detectable |
| Other heavy metals (incl. lead, cadmium, mercury, chromium VI, arsenic) | each below limit | not detectable |
No detectable banned azo dyes. No formaldehyde. No APEOs. The laboratory rates the sample as meeting requirements overall.The pH of 6.7 sits in the skin-friendly range.
The same chemical picture applies to our GOTS linen: azo dyes, formaldehyde, and APEOs not detectable; heavy metals not detectable.
5. Silk versus cotton — the direct comparison
| Property | Moonchild silk | Cotton | Advantage |
|---|---|---|---|
| Frictional resistance | 0.353 N | 0.462 N | Silk −24% |
| Coefficient of friction | 0.58 | 0.75 | Silk −23% |
| Absorbency at 5 min. | 68 mm | 38–42 mm | Silk |
| Evaporation at 30 min. | 20.02% | 15.91% | Silk |
| Water vapour permeability | 5474 g/m²/24h | 4890 g/m²/24h | Silk |
| Air permeability | 332 l/dm²/min | 490 l/dm²/min | Cotton |
| Rubbing fastness dry / wet | 5 / 5 | 4–5 / 4 | Silk |
| GOTS chemical screening | fulfilled | fulfilled | both |
For a pillowcase, the silk values add up: less friction, stronger capillary uptake, faster evaporation, high vapour transmission, colour that holds, and a clean chemical screen.
Lab numbers alone do not make a better night. They explain why our user study looks the way it does. Less friction means less mechanical stress on hair fibres and less pressure on sleep lines. Better wicking plus faster evaporation means moisture is taken up and released instead of sitting in the pillow. A pH of 6.7 and no detectable problem substances mean the fabric against your face is tested for skin contact.
Summary of Key Findings
- Silk has measurably lower friction. Frictional resistance is 24% below cotton; the coefficient of friction is 23% lower.
- The GOTS dye holds at the top grade. Rubbing fastness 5/5; the silk itself does not change color in the wash (grade 5). Transfer onto other fabrics is grade 5 or 4–5 — practically no staining.
- Banned harmful substances were not detectable. No azo dyes, no formaldehyde, no APEOs. pH 6.7.
- Silk absorbs moisture better. 68 mm wicking versus 38–42 mm for cotton — about 70% higher.
- Silk dries faster than cotton. 20.02% evaporation after 30 minutes, above the laboratory benchmark. Cotton sat below it at 15.91%.
- Breathability is 2.7× the specified value. Water vapour permeability: 5474 g/m²/24h against a laboratory minimum of 2000 — 174% above the benchmark.
- The laboratory rates the sample as meeting requirements. GOTS requirements fulfilled.
Study notes: The Moonchild Silk Pillowcase Lab Study 2026. Testing by CTL® GmbH Bielefeld. Results relate exclusively to the samples as received. Friction: CTL in-house method, silk versus cotton; “up to 24%” refers to frictional resistance (0.353 N versus 0.462 N). No friction comparison against linen was carried out. Colourfastness of the silk: DIN EN ISO 105-X12 (rubbing) and DIN EN ISO 105-C06 A1S (hand wash). Grade 5 = best rating on the grey scale. “Staining” measures whether silk dye transfers onto a standard adjacent fabric — not the colourfastness of the comparison cotton sample. Lightfastness was not part of this commission. Botanically dyed linen was not tested for rubbing or washing fastness in this order. Absorbency: AATCC 197 Option B / AATCC TM 213. Evaporation: ICOR Appendix 10. Water vapour permeability according to DIN 53122-1 (non-accredited test, marked * in the report). Nickel and zinc on the silk were measurable but below the stated limits. Benchmarks for wicking, evaporation, and breathability are laboratory experience values, not statutory limits. The overall GOTS assessment was fulfilled for all three samples.
