Tech Pack Essentials for Cut-Out Back Sports Bras

A tech pack built for a T-shirt will not produce a wearable cut-out back bra. The failure is predictable: the factory cuts what was drawn, the cut-out opens in a place that pulls against the shoulder blade, the strap convergence sits too high, and the first sample comes back looking right on the hanger and wrong on a body. A medium impact bra is a tensioned structure, and the tech pack is where that tension is defined. The following items are the ones most often missing from buyer-supplied packs.

Measurements and Tolerances

Specify the underband in both relaxed and stretched states, in millimetres, with tolerance. This single pair of numbers controls most of the fit outcome and most of the complaint volume. Add cup depth, cup width, wing height, strap length from the convergence point, and the hook overlap on each of the three rows.

For stretch garments, express tolerances as a percentage of the spec rather than a flat millimetre value. Underband relaxed of plus or minus 2 percent and stretched of plus or minus 3 percent is more workable than a blanket plus or minus 5 millimetres, which is too tight at XS and too loose at XL.

Defining the Cut-Out Geometry

A cut-out is not a decorative hole; it is a structural change that removes load paths from the back panel. Give both the shape outline and the position relative to a fixed anatomical landmark, and state the clearance requirement from the shoulder blade in millimetres. Specify how the edge is finished: turned and topstitched, bonded, or bound with a narrow elastic.

State what happens to the cut-out across the size range. If it scales proportionally with the grade, say so explicitly; if it should stay a fixed size, say that instead. Left unstated, the grader will make a decision for you and it will usually be the wrong one at the size extremes.

The Racerback Convergence

Specify where the two straps meet on the centre back, measured down from the neckline or up from the band, and the angle of convergence. This point determines how much the strap can migrate during rowing or cycling. Also specify strap width and whether the strap is a continuous cut piece or an inserted elastic, because the two behave very differently under load and after washing.

Stitch and Seam Specification

Name the stitch type per seam: flatlock or coverstitch for next-to-skin seams, overlock for internal edges, and the stitch density in stitches per inch. Flat seams reduce chafe complaints, and the seam allowance direction matters where the cut-out edge crosses a shoulder blade. Specify thread type, since a cotton-wrapped polyester thread behaves differently from a textured nylon thread in a high-stretch seam.

Elastic and Hardware

Give elastic width, modulus at a defined extension, minimum recovery after extension, and wash durability. For the closure, specify row count, hook count, hook gauge, coating, and a nickel-free requirement. Reference the compliance documents you expect: OEKO-TEX STANDARD 100 for fabric and trims, GRS transaction certificates for recycled content, and REACH or CPSIA declarations for metal hardware.

What to Attach

Include a graded measurement table, a construction callout sheet, a bill of materials with supplier or equivalent spec, label placement with exact distances, and a folding and packing instruction. The thinner the pack, the more decisions the factory makes for you.