Water-repellency is a feature obtained by applying a treatment that prevents water from adhering to the surface of the fabric.
It "slides off" without being absorbed, so the garment remains light, breathable and warm. Please note, this does not mean it is waterproof.
This treatment can be repeated to keep all its effectiveness. Use sprays that are applied to the outside, rather than additives used when washing the garment, which can damage the product's breathability.