A half-zip jersey has a zipper that extends only to mid-chest, giving you a smaller ventilation opening compared to full-zip options. This design shines in cool weather when you rarely need to dump heat quickly—you get just enough adjustability at the neck without the bulk of a full zipper running to your waist.
The trade-off is limited temperature control. If you're climbing hard or riding in warm conditions, you can't open up the jersey as much to cool down. Half-zip jerseys are also harder to pull on and take off since the opening is smaller.
Where half-zip really works well is for thermal and cold-weather jerseys, where you want a clean, streamlined look and won't be unzipping much anyway. They're also popular with riders who prefer the classic, minimal aesthetic. Just avoid half-zip for summer riding or hot climates—that's a common mistake that leaves you overheating.