According to an independent testing institute, fabric softener adheres to the fibres after the wash cycle and has a water-repellent effect. Whilst this is desirable, it also noticeably reduces the fabric’s breathability. The fibres no longer absorb sweat and cannot wick it away to the outside. However, the fabric softener is washed out of the fabric after a few washes. The functionality of the material is therefore restored. Nevertheless: avoid using fabric softener.