Brand proprietary membranes are manufacturer-developed waterproof-breathable technologies that can offer solid performance at a better price point than Gore-Tex. The catch is that performance varies—some brands come close to Gore-Tex levels, while others fall short in sustained wet conditions.
These membranes make a lot of sense if you're looking at mid-range to premium gloves and don't ride in relentless rain or wet snow all day. They typically handle normal resort skiing and mixed conditions just fine. The key is reading reviews for the specific glove model, since "proprietary" doesn't tell you much on its own.
If you consistently ski in the Pacific Northwest or other famously wet climates, Gore-Tex's guaranteed performance is worth the premium. But for drier regions or occasional riders, proprietary membranes deliver good value without overpaying for waterproofing you may not need.