A useful fabric brief does not need to be long, but it does need to make the important trade-offs visible. Begin with the garment and the wearer, not only a composition name.
First, describe the touch in comparison with a reference. Second, state the stretch direction and recovery expectation. Third, show the surface or visual finish the collection needs. Finally, identify the sales market and any test or documentation requirement that affects approval.
Volume, target timing and a physical swatch or garment make the next conversation more commercial. If a parameter is unknown, mark it as open rather than guessing; the development route can then be built around a clear decision.