Most ski hip protectors are designed to be worn next-to-skin or over just thin underwear, under all your other layers. This is the most common style—especially for compression-style impact shorts—because it keeps the pads locked in place right where you need them. When pads sit directly against your body, they're far less likely to shift during a fall, which is exactly when you need them most.
The main trade-off is warmth. Since these protectors fit snug against you with your base layer and ski pants on top, they can trap heat. If you run hot or ski in warmer conditions, look for models with moisture-wicking fabrics or ventilation zones to help manage that.
This style is ideal for most recreational skiers who want reliable, stay-put protection. Just make sure your ski pants have enough room to comfortably fit over the protector without feeling too tight or restrictive.