Sew-in bikini cups for swim and performance wear add smooth coverage under stretch fabrics. The quick-dry foam retains shape in water and stands up to repeated wear. Trim edges to fine-tune the fit inside lined tops; hand or machine-stitch into place. Ideal for refitting ready-made suits or finishing custom swim sets. Pack includes two size B cups. Suitable for home and classroom use; keep with core sewing notions for consistent results.