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.