Tech packs are also handy to use as a working document where all changes and revisions from the process of sampling through to production can be kept in one place. In a tech pack everything that goes into making the garment and instructions on how it should be made - fabrics, stitches, measurements, colors, and more, are listed along with photos and CADs (computer aid designs, basically sketches). You can think of it as a recipe, for clothes.
A tech pack, also known in the industry as a technical packet or specification sheets, is basically, super detailed instructions on how to make a garment during the sampling and manufacturing process.
