When dark leggings leave colour on shoes, seats or bags, the dye is transferring through friction, often while the fabric is damp with sweat. A washing fastness report does not cover that. It measures colour change and staining in a wash, not dye rubbing off onto a dry or damp surface. Ask the factory exactly which test the fabric passed before agreeing it is fine.

Ask for the full report, not a summary line, and check the test method, the conditions, the date and whether it was run on the bulk dye lot or on a lab dip. A pass on a light colour or an early sample says little about the navy lot that reached customers.

Test rubbing fastness, dry and wet

ISO 105-X12 tests colour fastness to rubbing. A white cotton rubbing cloth is rubbed on the fabric under set conditions, dry and wet, and the staining on the cloth is rated on a grey scale. Wet rubbing ratings are usually lower than dry ones, and wet rubbing matters for activewear because of sweat. Specify a minimum rating for both dry and wet rubbing, on bulk fabric from the actual dye lot.

Check washing fastness too

ISO 105-C06 tests colour fastness to domestic and commercial laundering and rates colour change and staining of adjacent fabrics. Poor washing fastness can show up as dye bleeding onto other items in the wash, which customers also complain about. Use the test condition that matches your care label, and wash garments with a named procedure such as ISO 6330 to check the finished product.

Why it happens

Transfer is often caused by dye that is not fully fixed or by excess dye left on the surface because washing-off after dyeing was cut short. With nylon blends, the dye route and after-treatment matter. Deep shades such as navy and black need the most care. Ask the mill for its after-treatment process for dark shades.

Before the next order

Write the rubbing and washing fastness requirements into the fabric approval, by colour, and ask for test reports for each bulk dye lot. If marks already appeared, a care note such as wash before first wear does not fix weak fastness, but it may reduce early complaints while you correct the fabric.

Keep the rubbing cloths from the approval test as a visual reference for future lots.