The question “what to wear under a jumper” isn’t just a personal style dilemma—it’s a core product development consideration for brands, gyms, and teams designing custom activewear. For the end-user, the right base layer impacts comfort, performance, and the final look. For the buyer or brand owner, it’s a decision that affects fabric sourcing, manufacturing complexity, cost, and how well your final product meets your customer’s needs. This guide breaks down the essential layers, fabrics, and features, then translates that into actionable intelligence for your next custom sportswear order.
Whether you’re sourcing for a high-performance outdoor line or a casual loungewear collection, understanding the function and form of under-jumper layers is critical. We’ll cover the technical standards, common material trade-offs, and the specific details you need to communicate to your factory to get samples and bulk production right the first time.
The Foundation: Base Layer & Mid Layer Fundamentals
Before selecting a specific garment, it’s helpful to categorize its role. In cold-weather or layered systems, apparel typically falls into three zones:
- Base Layer: Worn directly against the skin. Its primary jobs are moisture management (wicking sweat away) and thermoregulation. It should be seamless or flat-seamed to prevent chafing.
- Mid Layer: The insulating layer, often a fleece or lightweight knit, that traps warm air. This is frequently the “jumper” or sweater itself.
- Outer Layer: A shell (like a hardshell jacket or softshell) that provides wind and water protection.
For the purpose of this discussion, we are focusing on garments intended for the base layer and light mid-layer roles that go beneath a primary jumper or hoodie.
Key Base Layer Technologies & What They Mean for Sourcing
Modern base layers are engineered fabrics. Here are the dominant categories you’ll encounter and specify in a tech pack:
| Fabric Type | Key Properties | Best For | Production & Cost Notes |
|---|---|---|---|
| Merino Wool | Natural temperature regulation, odor-resistant, soft (low itch), good moisture wicking. | Multi-day wear, travel, high-end activewear, sensitive skin. | Higher raw material cost. Often blended (e.g., 50/50 with nylon) for durability. Requires careful finishing to prevent shrinkage. Specify wool micron count (e.g., 18.5µ) for quality. |
| Polyester (Moisture-Wicking) | Excellent wicking, quick-drying, durable, colorfast, cost-effective. | High-intensity sweat activities, gym wear, team uniforms, budget-conscious collections. | Vastly different quality levels. Look for specifications like “hydrophilic finish” or specific branded yarns (e.g., DuPont CoolMax®). Can retain odor if low-quality. |
| Polypropylene | Extremely low moisture absorption, fastest wicking and drying, very light. | Extreme cold, high-output aerobic activities (skiing, mountaineering). | Can melt under high heat (ironing, dryers). Less common in fashion-forward lines due to texture and melt-risk. Must be clearly specified. |
| Bamboo/Viscose Rayon | Soft, drapes well, natural feel, decent wicking, hypoallergenic. | Comfort-focused loungewear, yoga wear, casual base layers. | Durability can be lower than synthetics when wet. Processing involves chemicals; sustainability claims depend on manufacturer certification (look for OEKO-TEX®). |
| Silk | Ultra-light, excellent temperature regulation, luxurious feel. | High-end travel wear, delicate layering, minimalist fashion. | Expensive, delicate (requires hand-washing typically), less durable. Specialty sourcing required. |
Beyond Fabric: Critical Design & Fit Considerations
The fabric is just the start. The pattern, construction, and fit determine whether a layer is functional or frustrating.
Fit & Silhouette
A base layer must be form-fitting without being restrictive. Excess fabric creates bulk under a jumper and traps cold air. Key areas to specify:
- Length: Should tuck easily into pants/skirts without riding up during movement.
- Sleeve Length: Full-length is standard. For activities with arm movement (climbing, throwing), specify raglan or underarm gussets to prevent binding.
- Neckline: Crew neck is versatile. A high neck or mock turtleneck provides extra warmth and seals out drafts. A deep V-neck is for style but offers less thermal protection.
- Seam Placement: Flatlock seams are a must for high-movement zones. Avoid center-back seams on shirts if possible for comfort.
Features That Define a Performance Layer
When reviewing or creating a tech pack, don’t overlook these details:
- Thumbholes: Common in cold-weather gear. They prevent sleeve ride-up and provide extra hand coverage. Specify if they are functional or just a design element.
- Hem & Cuff Treatment: A silicone grip strip on the hem helps it stay tucked. Ribbed or elasticated cuffs seal out cold air.
- Odor Control: For polyester fabrics, specify if an antimicrobial treatment (e.g., Polygiene®, HeiQ) is required. This is a key differentiator for performance brands.
- Flat Seams & Tagless: Label placement (printed vs. tear-away tag) is a frequent specification from major brands to minimize irritation.
The Custom Manufacturing Perspective: What Buyers Need to Know
Shifting from consumer choice to production, here is the framework for sourcing and ordering these garments.
Specifying Your Order: The Tech Pack Checklist
A vague request for “warm shirts” will yield inconsistent results. Your tech pack must be precise. Use this checklist:
- Fabric Spec: Not just “polyester.” Specify the yarn type (e.g., 150gsm 100% polyester interlock), knit structure, and any special finishes (e.g., brushed interior, moisture-wicking, anti-pilling). Provide a physical fabric swatch if possible.
- Construction Details: Stitch type (e.g., 4-thread overlock), seam allowances, exact placement of thumbholes, hem type.
- Fit Model & Sizing: Provide a sample garment (a “fit sample”) on a model with known measurements. Specify the size set (e.g., XS-XXL) and grading rules.
- Trim & Labels: Specify all labels (main, care, size), their placement (printed, woven, tear-away), and thread colors. Don’t forget hanger tags and polybags.
- Color Standards: Use PANTONE® TPX or TCX codes for absolute color accuracy. Approving a lab dip (fabric dye sample) is non-negotiable before bulk production.
- Performance Testing: If making performance claims (e.g., “moisture-wicking,” “UV protection”), you must specify the test method. Common standards are set by ASTM International (e.g., ASTM D1805 for thermal insulation) or AATCC (e.g., AATCC 135 for dimensional change). Your factory should have relationships with testing labs.
Production Realities: MOQs, Lead Times, and Quality Verification
Understanding factory capabilities sets realistic expectations.
- Minimum Order Quantities (MOQs): These vary dramatically by factory and fabric. For standard polyester/spandex base layers in common sizes, MOQs can be as low as 500-1,000 pieces per style/color. For specialized fabrics (e.g., merino wool, intricate knits) or small size runs, MOQs may jump to 2,000-3,000+. Always ask for the MOQ breakdown per color and size.
- Lead Times: From approved fabric and fit sample, expect 4-8 weeks for bulk production. This extends significantly if new fabric needs to be sourced or dyed. Seasonal pressures (e.g., before winter) add time.
- The Sample Process: Never skip it. The typical sequence is: 1) Pre-production sample: Made with approved fabric, shows all details. 2) Fit sample: Made with similar fabric, sent for model fitting. 3) Production sample: The final approved sample that the production line uses as a template. Each approval stage adds time but prevents catastrophic bulk errors.
- Key Quality Markers to Inspect: Check samples and bulk for: consistent stitch density, no skipped stitches, secure seam ends, colorfastness (rub a white cloth on a colored area), print/embroidery clarity, and correct label content.
Making the Final Selection: A Decision Framework for Buyers
Use these guiding questions to narrow your choices and communicate effectively with your manufacturing partner.
- What is the primary use case? High-sweat training? Everyday casual layering? Extreme cold expedition? This dictates the fabric priority (wicking vs. insulation vs. softness).
- Who is the end-user? A fashion-conscious millennial will care about neckline and drape. A hockey team needs durability and easy care. A yoga studio wants softness and four-way stretch.
- What is the target price point? This is the ultimate governor. A $15 retail jersey cannot justify a $12/meter merino fabric. Map your fabric and construction costs to your desired wholesale and retail prices.
- What is the brand’s sustainability story? If this is a key pillar, you must source certified fabrics (GOTS for organic cotton, FSC for viscose, Responsible Wool Standard) and work with a factory that has credible certifications (e.g., Sedex, WRAP). Be prepared to verify and communicate this chain of custody.
- What are the care requirements? If your customer will machine-wash and tumble-dry, avoid delicate fabrics like silk or fine merino that require hand-washing. Specify “machine wash cold, tumble dry low” on the care label and test your sample accordingly.
FAQs for Buyers & Brands
What’s the biggest mistake brands make when ordering base layers?
Under-specifying the fabric. Ordering a “polyester shirt” leaves 1000 variables to the factory’s discretion, resulting in inconsistent hand feel, weight, and performance. Always get a physical fabric swatch approved in writing before proceeding.
Can I mix fabric types in one order to hit a price point?
Yes, and it’s a common strategy. You might use a premium merino blend for a “Pro” line and a standard performance polyester for a “Core” line. However, treat them as separate styles with separate tech packs. Mixing fabrics within a single garment (e.g., merino body with polyester sleeves) complicates production and is only feasible at very high volumes.
How do I ensure consistent color across different fabric types or production batches?
For absolute consistency, use the same fabric mill and dyehouse for all colors and subsequent orders. If that’s not possible, provide the mill with your PANTONE code and a physical lab dip from your first approved batch. For large orders spanning multiple production runs, consider scheduling dyeing in a single, large batch to guarantee uniformity.
What’s a realistic first-time MOQ for a custom base layer?
For a standard performance polyester or cotton/spandex blend in 3-5 colors and standard sizing (XS-XXL), many factories will accept orders between 800-1,500 pieces total. For more specialized fabrics (e.g., recycled nylon, organic cotton), expect MOQs of 1,500-3,000+. Your best approach is to be transparent about your budget and volume goals with potential suppliers; they can often suggest fabric alternatives that meet your cost targets.
Need custom versions of any style covered here? Our sportswear factory handles everything from tech pack review to bulk delivery. Request a sample or quote.