D3O is a "smart" material that stays soft and flexible while you're skiing but instantly hardens the moment it takes a hit. This means you get natural movement on the slopes without that bulky, restrictive feeling you might expect from serious protection. When you fall, the molecules in D3O lock together to absorb and disperse impact energy before your hip takes the brunt of it.
For most skiers, D3O offers the best balance of comfort and protection. It's especially great if you want to wear your hip protector all day without feeling like you're wearing hockey pads—D3O pads are typically thinner and more discreet under your ski pants than traditional foam options.
The main trade-off is price. D3O protectors cost more than basic EVA foam models, and they're not necessarily "better" than other premium materials like SAS-TEC, which offers similar impact performance with a slightly firmer feel. But if comfort and low-profile protection are priorities, D3O is tough to beat.