Bonded seams use heat-bonded tape or adhesive instead of traditional stitching to join fabric panels, creating an ultra-smooth, nearly seamless finish. This means less friction against your skin, which is a big win on long rides where even small irritations can become painful. They also offer a slight aerodynamic advantage since there's no raised stitching to catch air.
The trade-off is that bonded seams can be slightly less flexible at the joint and may not hold up as well over time compared to quality flatlock stitching. They're also typically found on premium-priced shorts, so you'll pay more for the technology.
Bonded seams make the most sense if you're logging serious miles, racing, or have sensitive skin that's prone to chafing. For shorter rides or casual commuting, quality flatlock stitching will serve you well at a lower price point. If you go with bonded, just be mindful that the seams may require gentler care to maintain their bond over time.