How to Wash a Hoodie

Cotton-Polyester Blend Chemistry and Shrinkage

Most hoodies are made from cotton-polyester blends (typical ratios: 80/20, 70/30, or 50/50 cotton/polyester) or from 100% cotton. Understanding how each fibre behaves under washing conditions explains the different care requirements and risks. Cotton fibres are natural cellulose polymers. The cotton boll grows as a flat ribbon that twists into a natural crimp during the plant's growth — this structural crimp is what gives cotton yarn its bulk and softness. During spinning into yarn and knitting into fabric, the fibres are held under tension in an elongated state. When the fabric is wet, water molecules form strong hydrogen bonds with the hydroxyl groups on the cellulose chains. This hydrogen bonding releases the tension that was holding the fibre elongated, and the fibre relaxes back toward its natural crimped length — this is fabric shrinkage. Heat accelerates this process by providing thermal energy that breaks the temporary bonds holding the fibre in its extended state. The result is a shorter, wider cotton fibre and a garment with smaller dimensions. Polyester fibres are synthetic thermoplastic polymers — polyethylene terephthalate (PET) — with no hydroxyl groups and no affinity for water. They do not absorb water and do not shrink under washing conditions. In a cotton-polyester blend, the polyester fibres resist the dimensional change the cotton fibres are trying to make, acting as an anchor. This is why a 50/50 blend shrinks significantly less than 100% cotton: the polyester constrains the movement of the cotton fibres. The two fabric constructions used for hoodie linings have different care implications. French terry has looped pile on the inside surface and a flat surface on the outside. The loops are left uncut — they create a lightweight, breathable, softly textured inner surface. French terry is less prone to pilling than fleece. Fleece is constructed from a similar looped structure, but the inner loops are brushed (mechanically agitated to raise the fibre ends) to create a soft, insulating pile. Fleece is warmer than French terry but the brushed fibre ends are prone to pilling and to shedding synthetic microplastic fibres in the wash — a washload of a fleece garment can shed thousands of synthetic microfibre particles into wastewater. A mesh laundry bag catches some of this but not all. Pre-shrunk hoodies have been through a hot wash cycle during manufacturing, releasing most of the garment's residual shrinkage potential before it reaches the customer. However, pre-shrunk does not mean shrink-proof. A typical pre-shrunk cotton hoodie can still shrink 3–5% in its first wash at home if washed hot. Over subsequent washes, the residual shrinkage decreases.