A lightweight hybrid core uses materials like balsa wood, paulownia, honeycomb structures, or even engineered air channels to dramatically cut weight from the ski. This matters a lot for touring because every ounce you save makes those long uphill climbs more manageable.
The tradeoff is that shedding weight usually means giving up some downhill performance. These skis can feel less stable at high speeds and may not absorb vibration as well as heavier wood-core skis when you're charging back down. They can also feel a bit twitchy in choppy snow compared to a burlier ski.
If you're doing long approaches or ski mountaineering where the ascent is the main focus, the weight savings is absolutely worth it. But if you're doing shorter laps and care more about ripping the descent, you might prefer a standard wood or wood-composite core that holds up better at speed and in variable conditions.