Thickness follows the design
There is no single best thickness for every shower. Panel dimensions, height, unsupported edges, door size, hardware, and the overall configuration determine what is appropriate for a specific enclosure.
3/8-inch glass
Three-eighths-inch tempered glass is widely used in frameless shower enclosures because it provides substantial rigidity with a refined appearance. It can be an excellent fit when the panel sizes, supports, and hardware are designed accordingly.
1/2-inch glass
Half-inch glass adds weight and rigidity and may be selected for certain large, tall, or minimally supported designs. The added weight also affects hinges, anchors, handling, and the structure supporting the enclosure.
Support and hardware matter
Glass thickness cannot be considered alone. Channels, clamps, headers, stabilizing bars, hinges, wall construction, and attachment locations work together as a system. A heavier panel is not automatically a better system.
Let the field conditions decide
After the finished opening is measured, the installer can review spans, clearances, support, and operation and recommend the glass and hardware combination that suits the project. That recommendation should come before fabrication.