Moderate arch support features a noticeable elastic or compression band through the midfoot of the sock. It creates a secure, supportive hug around your arch that keeps the sock firmly in place inside your ski boot — no bunching or slipping as you carve turns all day.
This level of support is especially great if you have high arches or tend to get foot fatigue during long days on the mountain. The compression through the arch can help reduce that tired, achy feeling by giving your foot a little extra stability. It's also popular with performance-oriented skiers who want a locked-in, responsive feel.
If you're an all-day skier looking for a balance between comfort and support, moderate arch support hits that sweet spot. Just remember that sock arch support is different from your boot's footbed or insole — the sock helps the sock stay put on your foot, while your insole supports your foot's structure directly.