Why do bras make lines under clothes?

Bras create lines under clothes when traditional construction features like cut-and-sew seams, underwire channels, and hardware are worn beneath clingy fabrics. Poor fit amplifies this issue: cups that are too small create spillover lines, while bands that are too tight or loose produce bulges and ripples that become visible under clothing.

The fabric of your outer garment plays a significant role too, as thin jerseys and rib knits cling closely to outline what's beneath.

Additionally, heat damage from dryers can warp foam cups and create permanent creases that print through even thicker tops.