EN 1621-1 Level 1 is a European safety standard that means the knee pad has been lab-tested to absorb significant impact energy. Specifically, when a 50 kN force hits the pad, no more than 35 kN gets through to your knee. It's verified protection, not just a manufacturer's claim.
For most skiers, Level 1 is the sweet spot. It's the standard you'll want for all-mountain skiing, freeride, park laps, and general resort riding. The pads offer solid impact protection while staying flexible and comfortable enough for all-day wear under your ski pants.
Where Level 1 falls short is FIS racing, where Level 2 certification is typically required. Level 2 pads block more force (under 20 kN transmitted) but are noticeably bulkier. If you're not racing competitively, Level 1 gives you certified protection without the extra bulk that can restrict movement on the hill.