Windstopper (now part of the Gore-Tex Infinium line) is a windproof, breathable, and water-resistant membrane from Gore, used in soft shells, fleeces, gloves, and hats. It blocks wind to preserve warmth while remaining highly breathable, but unlike Gore-Tex it isn't fully waterproof — it's built for cold, dry, windy conditions and active use rather than sustained rain.
Breathability is a fabric's ability to let water vapor (sweat) pass from the inside to the outside, keeping you dry from perspiration. In waterproof-breathable gear it's the counterpart to waterproofing, and it's measured by ratings such as MVTR (g/m²/24h) or RET (resistance — lower is more breathable). High breathability matters most for high-output activities.
A waterproof rating in millimeters (the hydrostatic head) measures how tall a column of water a fabric can withstand before water leaks through — the higher the number, the more waterproof. Roughly, 1,500 mm is minimally waterproof, 10,000 mm handles steady rain, and 20,000 mm+ resists hard rain and pressure. It's a key spec for comparing rain gear and tents.
DWR (Durable Water Repellent) is a chemical finish applied to the outer face fabric of waterproof-breathable garments that makes water bead up and roll off rather than soaking in. It isn't what makes a jacket waterproof — the membrane does that — but it keeps the face fabric from 'wetting out,' which would block breathability. DWR wears off and needs periodic reproofing.
eVent is a waterproof, breathable membrane built on expanded PTFE, known for its 'Direct Venting' technology that lets sweat vapor pass straight through the membrane rather than through an added layer. This gives it a reputation for high, immediate breathability, making it popular in high-output shells, though it traditionally requires diligent cleaning to stay breathable.
Gore-Tex is a waterproof, windproof, and breathable membrane used in outerwear and footwear. Its core is a thin film of expanded PTFE (ePTFE) with billions of microscopic pores far smaller than a water droplet but larger than a water-vapor molecule, so it blocks rain while letting sweat vapor escape. It's the best-known of the waterproof-breathable membranes.