ProECO Merino Wool Interlock: The Complete Guide to Wazoodle's Premium Merino Wool Interlock Fabrics

What ProECO Merino Wool Interlock Is and Why It Matters

ProECO Merino Wool Interlock is a double-knit fabric manufactured by AKAS Tex from 100% merino wool — 17–24 micron fiber diameter, fine enough to avoid triggering skin itch receptors. Double-knit interlock construction creates smooth, identical surfaces on both sides with no edge curling, making it the more structured and beginner-friendly of the two ProECO Merino Wool constructions.

The family spans two weights — 225 GSM and 285 GSM — and three variants: Standard in both weights, plus a FoodSAFE option with FDA certification for food-contact applications. All deliver the same merino fundamentals: natural temperature regulation across a 65–85°F active range, moisture management (30–35% absorption into the fiber core while maintaining a dry surface feel), and permanent keratin-based odor resistance that enables multi-day wear without washing.

Sourced from mulesing-free US merino flocks through the Chargeurs Wool partnership and processed through ProECO SustainSafe (chemical-free manufacturing). CPSIA certified, UPF 50+, Class 1 Flammability, Forever Chemicals-Free. Made in USA. Critical care requirement: cool water only (under 105°F) — hot water causes irreversible felting.

For how ProECO SustainSafe and Chargeurs Wool technologies work, see "What is ProECO SustainSafe Technology?" and "How Mulesing-Free Merino Wool Technology Works."

The Complete ProECO Merino Wool Interlock Lineup

ProECO Merino Wool Interlock includes three variants across two weight classes. Your first decision is weight; your second is treatment level.

Merino Wool Interlock — Double-Knit (225–285 GSM, 0.031–0.035" Thick)

W-221 ProECO Merino Wool Interlock 225 GSM: Medium-weight double-knit with 30%/10% stretch, 30–32" tubular width (60–64" cut open), 0.031" thick, 5% width / 10% length shrinkage. Smooth both sides with no edge curling — beginner-friendly cutting and construction. Customer-validated for period underwear, hiking shirts, headbands, and meditation shawls.
W-220 ProECO Merino Wool Interlock 285 GSM: The heaviest variant. 285 GSM at 0.035" thick with 30%/10% stretch and 60–64" width. Greater warmth and absorbency capacity than W-221. Customer-validated for doubled cloth diaper soakers, baby sleep sacks, lightweight sweaters, and mattress covers. Post-wash stretch increases to approximately 50% width / 25% length after initial stabilization. Note: W-220 shows a two-wash stabilization pattern — first wash produces primary shrinkage with slight felting, second wash confirms stable dimensions with no further change.
W-459 ProECO FoodSAFE Merino Wool Interlock: Interlock construction at 285 GSM with FDA food-contact certification per 21 CFR 177.1680 and 175.300. For food storage and preparation applications where the stable double-knit construction and merino's natural temperature properties serve insulated food carriers, bowl covers, and reusable storage requiring documented food safety.

Key Concept — Weight First, Treatment Second: Choose W-221 (225 GSM) for apparel and accessories where moderate weight provides structure. Choose W-220 (285 GSM) for maximum warmth and absorbency — baby items, diaper soakers, sleep sacks, and anything requiring doubled-layer construction. Choose W-459 only when your finished product contacts food directly and FDA certification is required for commercial sale.

All fabric specifications may vary ±10% due to textile industry manufacturing standards.

Choosing Your ProECO Merino Wool Interlock

All ProECO Merino Wool Interlock variants share 100% merino wool fiber, natural temperature regulation (65–85°F active range), keratin-based odor resistance, CPSIA certification, UPF 50+, and Class 1 flammability. Your decision has two dimensions: weight and treatment.

Choose by Weight

225 GSM (W-221) — The lighter interlock for apparel and accessories: period underwear, hiking performance wear, headbands, meditation shawls, and garments where moderate weight provides structure without bulk. The preferred choice for next-to-skin apparel and performance layering.
285 GSM (W-220) — The heavier interlock for maximum warmth and absorbency: doubled cloth diaper soakers, baby sleep sacks, lightweight sweaters, and mattress covers. Customers use two full layers through the entire soaker body for enhanced moisture capacity. The preferred choice for baby items and absorbent products.

Choose by Treatment

Standard (W-221, W-220) — For apparel, accessories, baby products, personal care, and any non-food-contact application. Covers the vast majority of Interlock uses.
FoodSAFE (W-459) — For products contacting food directly. FDA certification is required for commercial food-contact product sales. Choose when merino's natural temperature regulation and odor resistance serve food storage applications — insulated carriers, bowl covers, and reusable bags.

Dyeing note: Merino wool is a protein fiber requiring acid dyes — not the fiber-reactive dyes used for cotton and bamboo. Both Standard Interlock variants accept acid dyes well for custom color projects. The natural cream color is attractive enough that many makers leave it undyed, particularly for baby items.

Working With ProECO Merino Wool Interlock: Sewing and Construction Guide

ProECO Merino Wool Interlock is beginner-friendly compared to Jersey — the double-knit construction eliminates edge curl and lays flat for accurate cutting. The protein fiber care requirements remain the same: felting risk from heat and agitation, and wet weakness requiring careful drying.

Cutting and Layout

Pre-wash is mandatory — expect 10% length and 5% width shrinkage on first wash. Wash in cool water (under 105°F), lay flat to dry, then allow fabric to relax before cutting.
W-220 two-wash protocol: Always complete two full pre-washes before cutting W-220 — the second wash confirms stable dimensions with no further change. This predictable stabilization pattern is a characteristic of the heavier weight, not a defect.
Tubular format: All variants arrive tubular (30–32"). Cut open along one fold for flat yardage.
Both sides smooth (Interlock): Difficult to distinguish right from wrong side on all variants. Mark your chosen face with tailor's chalk before cutting.

Sewing Recommendations

Needle: Ballpoint or stretch needle, size 80/12–90/14, to prevent snagging protein fibers.
Stitch type: Stretch stitch or narrow zigzag — straight stitches risk popping under the natural wool stretch. Serge raw edges for clean finishing.
Thread: Polyester for durability through repeated laundering despite the all-natural fiber content.
Double-layer technique (W-220): Customers making diaper soakers use two full layers through the entire body — not just the wet zone — for enhanced absorbency throughout.
FoodSAFE integrity (W-459): Avoid chemical treatments, fusible interfacings, or adhesives that could compromise FDA certification for food-contact applications.

Pairing ProECO Merino Wool Interlock With Other Wazoodle Fabrics

ProECO Merino Wool Interlock serves as the skin-contact comfort layer in multi-layer builds, leveraging natural temperature regulation and odor resistance at the body interface. In standalone garments, it functions as the complete garment fabric.

Absorbent and Protective Builds

Cloth diaper soaker: ProECO Merino Wool Interlock 285 GSM (W-220) doubled for absorbent core. Merino's natural moisture capacity (30–35% of weight) combined with odor resistance provides extended-wear performance between washes.
Period underwear: ProECO Merino Wool Interlock 225 GSM (W-221, skin contact) → ProSoft 1 mil ECO-PUL (W-375, waterproof backing). Natural odor control supports extended-wear confidence.
Incontinence pad: ProECO Merino Wool Interlock (W-220, skin contact) → absorbent core → ProSoft ECO-PUL (barrier). The 285 GSM weight provides both comfort and moisture management at the skin surface.

Standalone Applications

Baby sleep sack: ProECO Merino Wool Interlock 285 GSM (W-220) as standalone — natural temperature regulation prevents overheating during sleep, CPSIA certification for infant safety.
Performance apparel and accessories: W-221 as standalone for hiking shirts, headbands, meditation shawls, and base layers where structured knit and moderate weight provide performance without bulk.

Your results may vary based on product design and construction. For complete build guidance on specific projects, see the relevant Application Discovery articles.

Common Applications for ProECO Merino Wool Interlock

ProECO Merino Wool Interlock serves apparel, baby, personal care, and absorbent product applications where natural fiber performance replaces chemical treatments. Use 1–2 layers depending on application requirements.

Baby clothing and sleep sacks — The primary application for W-220. CPSIA certification with chemical-free processing supports infant products. Natural temperature regulation prevents overheating during sleep. 17–24 micron fiber softness meets sensitive baby skin standards.
Cloth diaper soakers — W-220 at 285 GSM used doubled through the entire soaker body for enhanced absorbency. Merino's natural odor resistance extends wear time between washes — a significant advantage over cotton soakers.
Period underwear and incontinence products — W-221 validated for period underwear construction where natural odor control and moisture management matter for extended-wear confidence.
Hiking apparel and outdoor performance wear — W-221 for hiking shirts and headbands where moisture management, temperature regulation, and multi-day odor control during activity matter.
Meditation shawls and accessories — Both W-221 and W-220 serve contemplative wear and cold-weather accessories. The stable double-knit construction provides clean drape without edge-finishing complexity.
Lightweight sweaters and structured knitwear — W-220 for lightweight sweaters and layering pieces where greater weight provides warmth and body.
Mattress covers — W-220 for mattress protection where absorbency and natural odor resistance serve extended-wear bedding applications.
Food storage (W-459 FoodSAFE) — Insulated carriers, bowl covers, and reusable storage where the stable double-knit construction and merino's natural temperature properties combine with FDA-certified food safety.

For complete build guides for specific applications, see the relevant Application Discovery articles.

ProECO Merino Wool Interlock Certifications

All variants hold the same core safety certifications through ProECO SustainSafe processing. W-459 adds FDA food-contact certification.

Safety Certifications

CPSIA Certified: Children's product safety compliance (lead, phthalates, BPA testing)
Flammability Class 1: Per 16 CFR Part 1610 — general apparel classification suitable for children's garments and sleepwear
California Proposition 65 Compliant
EU REACH SVHC and RoHS 10 Compliant
UPF 50+: Blocks 98% UV radiation
Made in USA: EPA/OSHA manufacturing standards
Chargeurs Wool Certified: Mulesing-free US merino sourcing with verified ethical animal welfare practices
FDA Food Contact (W-459 only): Certified per 21 CFR 177.1680 and 175.300 for repeated-use food contact

Chemical-Free Verifications

Forever Chemicals-Free: No PFAS, PFOS, PFOA, PTFE detected
BPA-Free, Phthalate-Free, Lead-Free: Tested per CPSIA standards
Synthetic-Free: 100% natural protein fiber — no synthetic additives
pH 7.4 (Neutral): No acidic or basic residues
Color Fastness 4.5: Exceeds standard 3–4 rating

Fabric vs. Finished Product: CPSIA certification of the fabric does not automatically certify your finished product. Finished children's products may require independent testing depending on your product category and sales channels.

ProECO Merino Wool Interlock Care

ProECO Merino Wool Interlock requires protein-fiber-specific care that differs fundamentally from every other ProECO fabric family. The defining constraint: cool water only — hot water causes irreversible felting that cannot be undone.

Washing

Hand wash or gentle machine cycle in cool water only — maximum 105°F. Merino loses 25–30% strength when wet, so handle gently without wringing or twisting. Use mild detergent without enzymes. W-220 customers report that warm water with low-heat tumble drying produces workable results, but cool water maximizes fabric lifespan.

Drying

Lay flat to dry — never hang. Wet wool stretches under its own weight, and hanging causes permanent distortion. Remove excess water by gently pressing between towels. Hot iron acceptable with press cloth if pressing is needed.

What to Avoid:

Never use hot water — temperatures above 105°F cause irreversible felting and up to 30% shrinkage that cannot be undone. Never use fabric softeners — they coat protein fibers, destroying natural moisture management. Never use chlorine bleach — it degrades keratin fiber structure. Oxygen bleach is acceptable for all variants.

Pre-Wash Requirements

Pre-wash entire yardage before cutting — expect 10% length and 5% width shrinkage. W-220 requires two pre-washes to reach stable dimensions. Always test a small piece first. Pilling is normal in high-friction areas after 10–20 wears — remove gently with a fabric shaver.

For complete care protocols, see "How to Care for Organic, Bio-Based, and Recycled Content Fabrics."