The same washing machine programme can freshen up a cotton T-shirt but ruin a wool sweater or silk shirt. Hot water is not a universal way to achieve better cleaning, and with some fabrics it accelerates shrinkage, fading and deformation.
The most important rule is that the care label on the specific garment takes precedence over general recommendations. If there is no label or the instructions are unclear, the safer choice is cold water, a gentle cycle and air-drying.
Wool, Cashmere and Knits
Wool is among the materials most easily damaged by the combination of heat, water and vigorous spinning. The fibres can shrink, felt and change shape. The same applies to cashmere and many knitted garments.
The American Cleaning Institute recommends choosing a cold wash if in doubt. When washing by hand, the garment should not be rubbed or wrung. After rinsing, excess water should be removed by gently pressing the garment in a towel, and the knitwear should be left to dry flat.
Silk, Satin and Viscose
Silk is sensitive to excessive heat. Hot water can cause shrinkage, loss of shine and weakening of the fibres. If the care label permits washing, the usual gentler option is cold water, a delicate cycle or hand washing with a detergent for delicate fabrics. Silk should not be wrung and is generally dried away from direct sunlight.
Viscose and rayon should also be washed more carefully, most often in cold water. Heat and strong mechanical action can alter the garment’s size and shape. Lace and satin are not necessarily made from the same type of fibre, but they are treated as delicate fabrics when this is indicated on the care label.
Elastane, Sportswear and Swimwear
Elastane, also known as spandex, loses its elasticity more quickly with frequent exposure to high temperatures. That is why sportswear, leggings, underwear and swimwear containing these fibres are generally washed in cold water and air-dried, away from intense heat.
“Cold water is often the gentler choice because it is less likely to cause dyes to run, fibres to shrink or elastic materials to break down,” says Noah Pinsonno, an analyst at the home care and cleaning laboratory of the Good Housekeeping Institute.
Colours and Denim
Hot washing is also unsuitable for many brightly coloured or dark garments. High temperatures can accelerate fading and dye transfer, especially in new items. Denim also holds up better when washed in cold water, which limits colour loss and the risk of shrinkage.
Cotton and linen generally tolerate higher temperatures better than wool and silk. This does not mean, however, that every cotton or linen garment should be washed hot. For all materials, the care-label symbols and the maximum temperature specified by the manufacturer remain the deciding factors.
Sources: goodhousekeeping.com