When you pick up a fleece jacket, you're holding what is fleece made of: a synthetic fabric constructed primarily from polyester plastic. Despite its name suggesting sheep's wool, modern fleece is almost entirely man-made, engineered to mimic wool's warmth whilst offering advantages natural fibers cannot match.
Understanding fleece composition matters because this ubiquitous fabric appears in everything from outdoor gear to blankets, yet many people remain unclear about its actual material origins and manufacturing process.
What Is Fleece Made Of?
Fleece fabric is manufactured predominantly from polyester, a synthetic polymer derived from petroleum-based chemicals. The material composition breaks down as follows:
Standard Polyester Fleece
Traditional fleece consists of 100% polyethylene terephthalate (PET), the same thermoplastic polymer used in plastic bottles. Manufacturers melt PET pellets and extrude them through spinnerets to create continuous synthetic fibers. These fibers are then knitted into fabric and mechanically brushed to produce the characteristic soft, fuzzy texture.
Recycled Polyester Fleece
An increasing proportion of fleece products use recycled polyester sourced from post-consumer plastic bottles. The manufacturing process involves:
- Collecting and cleaning used PET bottles
- Shredding plastic into small flakes
- Melting and filtering the material
- Extruding new polyester fibers
- Processing these fibers identically to virgin polyester
Recycled fleece performs identically to virgin polyester fleece whilst reducing petroleum dependency and plastic waste.
Blended Fleece Fabrics
Some fleece incorporates additional materials to modify performance characteristics:
- Cotton-polyester blends: Typically 80% polyester, 20% cotton for enhanced breathability
- Spandex blends: 2-5% elastane added for stretch and form retention
- Wool-synthetic blends: Combining natural wool fibers with polyester for specific applications
Natural fleece—referring to wool directly from sheep—represents an entirely different product category from synthetic fleece fabric, despite sharing the same name.
How Fleece Is Made: The Manufacturing Process
Understanding fleece production clarifies why this synthetic material possesses its distinctive properties.
Step 1: Polymer Creation
Manufacturers combine purified terephthalic acid with ethylene glycol through a chemical process called polymerization. This reaction produces long molecular chains of polyethylene terephthalate. For recycled fleece, this step is replaced by melting down cleaned plastic bottles.
Step 2: Fiber Spinning
The PET polymer is heated to approximately 260-290°C until molten, then forced through spinnerets—metal plates containing thousands of tiny holes. As the liquid polymer emerges, it cools and solidifies into continuous synthetic fibers. Manufacturers control fiber thickness by adjusting spinneret hole size and extrusion speed.
Step 3: Knitting the Base Fabric
Unlike woven fabrics, fleece uses a knitting process that creates interlocking loops of polyester yarn. This knitted structure provides inherent stretch and flexibility. Most fleece uses a circular knitting process producing seamless tubular fabric.
Step 4: Brushing and Napping
This stage creates fleece's signature texture. Mechanical brushes with fine wire teeth rake across the knitted fabric surface, pulling fibers outward to form a raised pile. The brushing may occur on one side (single-sided fleece) or both sides (double-sided fleece). The density and length of this pile determines the fleece's warmth and softness.
Step 5: Finishing Treatments
Final processing may include:
- Anti-pilling treatments to reduce bobbling
- Water-repellent coatings for outdoor applications
- Anti-static treatments
- Dyeing to achieve desired colours
- Heat stabilization to prevent shrinkage
Types of Fleece and Their Material Composition
Fleece categories reflect differences in fiber weight, pile structure, and sometimes material blends.
Polar Fleece
The original and most common fleece type, polar fleece features medium-weight polyester fibers (typically 200-300 GSM—grams per square meter) with a dense, evenly brushed surface. The material consists of 100% polyester or recycled polyester, engineered specifically for warmth-to-weight efficiency.
Microfleece
Manufactured from finer polyester fibers (usually 100-200 GSM), microfleece produces a thinner, lighter fabric suitable for layering. The reduced fiber diameter creates a softer hand feel whilst maintaining polyester's core properties. Material composition remains identical to polar fleece—only fiber fineness and fabric weight differ.
Sherpa Fleece
Also called "pile fleece," sherpa mimics sheepskin appearance through specialized brushing that creates longer, more irregular pile texture. The base material remains polyester, but the mechanical finishing process differs significantly, producing a fluffier, more textured surface resembling natural wool fleece.
Technical Fleece Blends
Performance-oriented fleece often incorporates additional synthetic fibers:
- Stretch fleece: 92-95% polyester with 5-8% spandex
- Grid fleece: 100% polyester with a waffle-textured interior for improved breathability
- Windproof fleece: Polyester exterior bonded to a polyurethane membrane
Properties of Fleece: Why Polyester Works
The synthetic composition of fleece creates specific performance characteristics.
Insulation Without Weight
Polyester fibers trap air within the raised pile structure. Since air is an excellent insulator, this creates warmth without requiring heavy material. The synthetic fibers maintain loft better than many natural materials, ensuring consistent air-trapping capacity.
Moisture Resistance
Unlike wool or cotton, polyester is hydrophobic—it does not absorb water. When fleece becomes wet, moisture sits on fiber surfaces rather than penetrating the material. This property allows fleece to:
- Dry rapidly (typically 2-4 hours)
- Retain insulating properties when damp
- Resist becoming heavy when exposed to precipitation
Breathability
The knitted construction and synthetic fiber composition allow water vapor to pass through whilst resisting liquid water. This enables perspiration to escape during physical activity, preventing the dampness that compromises warmth.
Durability and Shape Retention
Polyester's chemical stability means fleece resists:
- Degradation from UV exposure
- Weakening from repeated washing
- Stretching and sagging over time
- Damage from mildew or moths
Soft Texture
The mechanical brushing process and the smooth surface of polyester fibers combine to create a soft hand feel without the potential scratchiness of some natural wools.
Fleece vs Other Materials: Material Comparison
Understanding compositional differences clarifies when fleece outperforms alternatives.
Fleece vs Wool
Material basis: Fleece is polyester plastic; wool is protein-based animal fiber
Insulation when wet: Fleece maintains 80-90% warmth when damp; wool retains approximately 70-80%
Drying time: Fleece dries in 2-4 hours; wool requires 8-24 hours
Weight: Fleece provides equivalent warmth at 30-40% less weight
Odour retention: Wool naturally resists odours; polyester fleece absorbs and retains body odour more readily
Sustainability: Wool is renewable and biodegradable; polyester fleece is petroleum-derived and persistent
Cost: Fleece typically costs 40-60% less than comparable wool products
Fleece vs Cotton
Material basis: Fleece is synthetic polyester; cotton is natural plant cellulose
Water absorption: Cotton absorbs up to 25 times its weight in water; fleece absorbs minimal moisture
Insulation: Fleece maintains warmth when wet; cotton loses virtually all insulating capacity
Durability: Polyester fleece resists pilling and wear better than cotton
Breathability: Cotton offers superior breathability in warm conditions
Environmental impact: Cotton requires intensive water and pesticides; fleece contributes to microplastic pollution
Synthetic Fleece vs Natural Fleece (Wool)
These represent fundamentally different materials that happen to share a name. Synthetic fleece refers to manufactured polyester fabric. Natural fleece means wool directly from sheep, which retains the crimped fiber structure and lanolin coating. They serve similar functions but through entirely different material properties and manufacturing processes.
Environmental and Sustainability Considerations
The polyester composition of fleece creates specific environmental implications.
Microplastic Shedding
During washing, synthetic fleece releases microscopic plastic fibers. Research indicates a single fleece garment may shed 1,900-2,000 fibers per wash. These microplastics:
- Pass through wastewater treatment systems
- Enter aquatic ecosystems
- Accumulate in marine organisms
- Persist indefinitely in the environment
Mitigation strategies include washing less frequently, using guppybag filters, and choosing tightly-constructed fleece with anti-shedding treatments.
Recycled Polyester Benefits
Fleece manufactured from recycled plastic bottles offers measurable advantages:
- Reduces petroleum extraction by 50-60% compared to virgin polyester
- Diverts plastic bottles from landfills and oceans
- Requires 30-40% less energy during production
- Produces 30-35% fewer carbon emissions
However, recycled fleece still sheds microplastics identically to virgin polyester fleece.
Longevity Versus Biodegradability
Polyester fleece presents an environmental trade-off:
Advantages: Extreme durability means one fleece garment can last 10-20 years with proper care, reducing overall consumption. The material resists degradation, maintaining performance throughout its lifespan.
Disadvantages: When eventually discarded, polyester fleece persists in landfills for 200+ years without decomposing. Unlike wool, which biodegrades completely, synthetic fleece becomes permanent waste.
Comparative Sustainability
Fleece may represent a more sustainable choice than alternatives when:
- Replacing multiple short-lived cotton or wool garments
- Used in conditions where natural fibers would fail (marine environments, high precipitation)
- Manufactured from recycled materials and worn for many years
- Washing frequency is minimized through spot cleaning
Common Uses of Fleece
The material composition makes fleece suitable for specific applications.
Clothing
- Outdoor jackets: The polyester's moisture resistance and lightweight insulation suit active outdoor use
- Mid-layers: Fleece's breathability allows it to function beneath waterproof shells
- Casual wear: Hoodies, pullovers, and sweatshirts capitalize on softness and comfort
- Base layers: Microfleece provides next-to-skin warmth
Home Textiles
- Blankets: The soft texture and warmth make fleece popular for throws and bedding
- Pet bedding: Durability and easy washing suit animal applications
- Craft materials: Fleece's non-fraying edges and availability make it useful for no-sew projects
Technical Applications
- Linings: Fleece provides insulation inside gloves, boots, and jackets
- Sleeping bag insulation: Synthetic fleece maintains warmth in damp conditions
- Emergency blankets: Quick-drying properties suit medical and rescue contexts
Frequently Asked Questions
Is fleece made from plastic?
Yes, fleece is made from polyester, which is a plastic polymer derived from petroleum. The material composition is identical to that used in plastic bottles—polyethylene terephthalate (PET). Some fleece uses recycled plastic bottles as the source material, but the resulting fabric is still plastic-based polyester.
Is fleece natural or synthetic?
Fleece fabric is synthetic, manufactured entirely from man-made polyester fibers. Whilst the term "fleece" originally referred to wool from sheep, modern fleece clothing and blankets are almost exclusively synthetic. Some products blend polyester with natural fibers like cotton or wool, but pure fleece is 100% synthetic material.
Is fleece warmer than wool?
Fleece and wool provide comparable warmth when dry, but their material composition creates different performance in wet conditions. Fleece maintains more warmth when damp because polyester doesn't absorb water. Wool absorbs moisture but retains some insulating capacity. For equivalent warmth, fleece weighs significantly less than wool, making it warmer per gram of material.
Is recycled fleece safe?
Recycled fleece is safe for normal use. The manufacturing process melts and purifies plastic bottles, removing contaminants and creating polyester fiber chemically identical to virgin material. Recycled fleece performs equivalently to standard fleece in warmth, durability, and comfort. The main concern with all fleece—recycled or virgin—is microplastic shedding during washing, not safety of the material itself.
Does fleece shed microplastics?
Yes, polyester fleece sheds microscopic plastic fibers during washing. Research shows fleece releases 1,900-2,000 microplastic fibers per wash cycle. These pass through wastewater systems into waterways. To minimize shedding: wash fleece less frequently, use cold water, install a microfiber filter, or use a Guppybag. Fleece constructed with tighter knitting and anti-pilling treatments sheds fewer fibers than loosely-constructed fabric.
Fleece fabric's composition—primarily polyester plastic—explains both its remarkable performance characteristics and its environmental considerations. Understanding what fleece is made of enables informed choices about when this synthetic material represents the best option for warmth, durability, and practicality.