How to Wash Polar Fleece
Polar fleece is polyester microfibre brushed into pile — each wash sheds 500,000 to 1.7 million microplastic fibres. A mesh laundry bag captures 25–54% of them before they reach the drain. Cold gentle wash inside out; low-spin cycle. Polyester pile glazes permanently above 70–80°C, so tumble dry on low only. Never use fabric softener on DWR-treated fleece.
The Chemistry
Polar fleece is a polyester knit fabric with a mechanically brushed pile surface. The base fabric is typically a plain jersey or tricot knit of polyethylene terephthalate (PET) polyester; after knitting, wire-covered rollers or card clothing drums brush the surface of the fabric, raising loose fibre ends from the knit ground to form the characteristic soft pile. Polartec (formerly Malden Mills) pioneered this construction in 1979, and "polar fleece" now describes the entire category. This construction is distinct from generic "fleece" in that polar fleece pile is produced from very fine microfibre PET yarns — individual fibre diameters are often 0.5–2 denier, substantially finer than standard polyester. The microfibre construction increases the total fibre surface area per unit weight, which improves thermal insulation (more dead-air trapping within the pile) and surface softness. The same microfibre construction is the source of polar fleece's most significant environmental issue: microplastic shedding. When polar fleece is washed, mechanical agitation in the drum breaks loose pile fibres — individual polyester filaments detach from the brushed surface and become suspended in the wash water. Because these fibres are typically less than 5mm in length and are polyester (non-biodegradable), they are defined as microplastics. Studies have measured between 500,000 and 1.7 million fibres shed per single wash from a polar fleece jacket. Conventional wastewater treatment plants capture 70–99% of microplastics, but the remaining fraction passes into waterways and accumulates in marine ecosystems. Cold water washes reduce the number of fibres shed compared to hot water washes — cold water causes less fibre-level stress and fewer complete fibre breaks. Mesh laundry bags (Guppy bag) and washing machine filter balls (Cora Ball) capture 25–85% of shed fibres before they reach the drain. A slow, gentle, low-spin cycle also generates less fibre-on-fibre abrasion than a high-speed cycle. Pilling in polar fleece occurs via the same mechanism as in other textured fabrics: loose pile fibre ends exposed on the surface entangle under mechanical agitation, twist together, and form small stable fibre balls anchored to the ground fabric. Anti-pill fleece variants (such as Polartec Classic 200 Anti-pilling) use a tighter knit ground fabric or a secondary brushing and shearing step to remove the most vulnerable loose fibre ends before the garment is sold. These variants pill less but shed approximately the same number of fibres per wash. The glass transition temperature (Tg) of PET polyester is approximately 70–80°C. Above the Tg, amorphous PET polymer chains gain mobility, and the pile fibres can soften, compress, mat against each other, and permanently fuse. This is pile glazing — the hallmark of a polar fleece garment damaged by excessive dryer heat. The matt, hard, shiny patches are permanent. Tumble dry on the low or air-dry setting only. Hot ironing polar fleece causes the same glazing instantly; polar fleece must never be ironed. DWR (durable water repellent) coatings are applied to some polar fleece garments intended for outdoor use — typically softshell fleece used as a mid-layer in rain or wet conditions. DWR coatings are typically fluoropolymer or non-fluorinated polymer treatments applied to the garment surface. After washing, DWR performance can be partially restored by tumble drying on low heat — heat reactivates the polymer chains and restores their orientation on the fibre surface. Fabric softener deposits a thin coating on the pile surface that blocks DWR reactivation, so fabric softener must never be used on DWR-treated fleece garments.
Step-by-step
- 1
Cold wash only — cold water reduces microplastic fibre shedding and prevents pile glazing
Hot water causes more fibre-level stress in the polyester pile and produces more complete fibre breaks, increasing microplastic shed count. Cold or 30°C washing reduces shed fibres by an estimated 30% compared to warm washing. Cold water also keeps well below the polyester glass transition temperature of 70–80°C — pile fibres cannot begin to soften at cold temperatures. Use a standard gentle cycle with a short wash time.
- 2
Wash inside out in a mesh laundry bag — two independent mechanisms to reduce shedding
Turning the garment inside out means the more vulnerable pile surface is sheltered from direct drum contact. A mesh laundry bag (such as a Guppy bag) is an additional filter layer — the dense mesh traps fibres that shed during washing before they reach the washing machine drain. Studies show mesh bags capture 25–54% of shed fibres. A Cora Ball or similar filter device placed in the drum captures an additional 25–31%. Using both the bag and a device is more effective than either alone.
- 3
Use a low-spin cycle — high spin creates more interfibre abrasion and breaks more fibres
High spin speeds force the garment into the drum wall at high force during spin extraction, compressing the pile and creating high-friction contact between fibres. Reducing spin speed to 600–800 rpm rather than 1200–1400 rpm lowers the mechanical stress on pile fibres and reduces total fibre break count per wash cycle. Some machines have an eco or low-impact cycle that combines low agitation with reduced spin speed.
- 4
Never use fabric softener — it blocks DWR reactivation and reduces pile loft
Fabric softener deposits a waxy cationic surfactant layer on the pile surface. On polar fleece, this has two effects: it reduces the thermal insulation efficiency by coating and matting the pile fibres, and it physically blocks the DWR polymer layer from reactivating properly when heat is applied in the dryer. For DWR-treated outdoor fleece, omitting fabric softener is especially important. Use a small dose of gentle liquid detergent without softener.
- 5
Tumble dry on low heat only — polyester pile glazes permanently above 70–80°C
PET polyester has a glass transition temperature of approximately 70–80°C. Above this, the pile fibres soften, compress together, and fuse — pile glazing is permanent and cannot be reversed. Most tumble dryer high-heat settings reach 70–85°C inside the drum, which is directly within the risk range. Use the low or air-dry tumble setting. If drying DWR-treated fleece, tumble dry low for 10 minutes to reactivate the DWR coating, then remove and air dry. Never iron polar fleece.
- 6
Wash polar fleece less frequently — air it out between washes to reduce total fibre shed
Every wash cycle removes thousands of fibres from the pile surface and permanently reduces the pile density of the garment over time. Polar fleece used as an insulating mid-layer often does not need washing after every use — the outer shell layer takes the dirt and the base layer takes the sweat. Air the fleece out in a ventilated area overnight to remove odour between washes. Wash only when visibly dirty or genuinely odorous.
Polar fleece washing guide by type
| Type | Wash | Dry | Pilling risk | Microplastic | Notes |
|---|---|---|---|---|---|
| Standard polar fleece (Polartec Classic) | Cold 30°C gentle inside out in mesh bag | Tumble dry low or air dry | Medium-high without mesh bag | High | Low spin; no fabric softener; use Guppy bag |
| Anti-pill polar fleece (Polartec anti-pilling) | Cold 30°C gentle inside out in mesh bag | Tumble dry low or air dry | Low — secondary brushing removes loose ends | Similar to standard fleece | Pills less but sheds similar fibre count |
| DWR-treated softshell fleece | Cold 30°C; no fabric softener | Tumble dry low 10 min to reactivate DWR, then air dry | Low — tighter surface construction | Medium | Fabric softener permanently blocks DWR reactivation |
| Fleece blankets / throws | Cold 30°C gentle in mesh bag if possible | Tumble dry low or air dry flat | Low (lighter pile density) | Very high — large surface area | Mesh bag especially important for large surface area items |
| Fleece-lined jackets (fleece + shell) | Cold 30°C gentle inside out; check shell care label | Tumble dry low or air dry | Low — pile is sheltered inside garment | Low — inner pile is protected | Shell care label typically governs — follow the most restrictive instruction |
Frequently asked questions
How do I reduce microplastic shedding when washing fleece?
Three interventions reduce microplastic shedding: (1) Wash in a mesh laundry bag such as a Guppy bag — the dense mesh traps shed fibres before they reach the drain, capturing 25–54% of shedding. (2) Add a Cora Ball or similar filter device to the drum — captures an additional 25–31%. (3) Use a cold, gentle, low-spin cycle — cold water reduces fibre-level stress and fewer complete fibre breaks occur; low spin reduces drum-wall abrasion pressure. Using all three together is significantly more effective than any one measure alone. Washing less frequently also reduces total lifetime shedding.
Can I tumble dry polar fleece?
Yes, on low heat only. PET polyester has a glass transition temperature of approximately 70–80°C — above this, the pile fibres soften, compress, and permanently fuse (pile glazing). Most tumble dryer high-heat settings reach 70–85°C inside the drum, which is directly within the risk range. Use the low or air-dry tumble setting only. For DWR-treated outdoor fleece, 10 minutes on low heat after washing helps reactivate the DWR coating — then remove and finish air drying. Never use a high heat setting on polar fleece.
Why does my fleece pill and can I prevent it?
Pilling occurs when loose pile fibre ends on the brushed surface entangle under mechanical agitation, twist together, and form small stable fibre balls anchored to the ground fabric. Prevention: wash inside out (pile surface sheltered from drum), use a mesh laundry bag (reduces pile-to-drum contact), and use a low-spin cycle (less mechanical abrasion). Anti-pill fleece variants (Polartec anti-pilling) have been through an additional brushing and shearing step that removes the most vulnerable loose ends before sale — these pill significantly less. Existing pills can be removed with a fabric shaver, which cuts them off without pulling fibres from the ground fabric.
Why does polar fleece lose its softness after washing?
Two main causes: (1) Pile matting from fabric softener deposits — the waxy surfactant layer coats and compresses pile fibres, reducing their ability to stand upright and create the soft airy surface. This is avoided by never using fabric softener on polar fleece. (2) Pile glazing from excess dryer heat — above the polyester glass transition temperature (70–80°C), pile fibres soften and fuse permanently into a hard, shiny surface. This is permanent and irreversible. A third minor cause is progressive pile fibre loss from repeated washing — the garment becomes slightly thinner over time as shed fibres are not replaced.