Moving from 100 percent cotton to a cotton-polyester blend changes how a tee behaves in washing, wear and feel. Polyester is a synthetic fibre that absorbs little water and holds its shape, while cotton absorbs water and shrinks. In general a blend can reduce shrinkage and wrinkling, but the real effect depends on the yarn, knit, finishing and blend ratio, so it has to be tested on the actual fabric.

Washing and shrinkage

Wash the blended fabric and garments with a named procedure such as ISO 6330 and measure the length and width change, then compare with your cotton tee. Do not assume the result: knit construction and relaxation in finishing matter as much as the fibre. Include the drying method you plan to allow.

Pilling and surface

Blends with polyester can pill, because strong polyester fibres hold the little balls of fibre on the surface instead of letting them wear off. Test pilling after washing with a Martindale method such as ISO 12945-2 and compare with the cotton control. Spun and combed yarns of the same blend can give different results.

Feel and comfort

A blend feels different against skin and dries differently from cotton. Ask for wear samples and judge on the same task your customer will do. Check weight with ASTM D3776 so that you are comparing like with like, and check how the fabric handles odour and moisture in wear, by trial, not by claim.

Dyeing and colour

Cotton and polyester take different dyes, so blends are dyed in more than one step, or the polyester is left to give a heathered look. Ask the mill what it does for your colours, and check colour consistency lot to lot. Some blends show a different shade in daylight than under store lights.

The label

Under the FTC Textile Rules, 16 CFR Part 303, the label names the fibres by generic name and gives percentages by weight in order of predominance. Terms such as CVC are trade shorthand and are not labels. Make sure the label matches the fabric test report. Fibre percentages on a label should come from the fabric’s actual composition, so ask the mill to confirm the ratio for each lot, particularly where a heather effect is made by mixing yarns, since the real ratio can differ from colour to colour in the same style and each colour may need its own check.