ULF, or Ultra Light Fusion, construction uses a reinforced PVC material that is heat-fused directly to the interior drop stitch core. The CX, or cross-weave, construction uses the same type of fusion construction but with an upgraded internal core that uses less material (making it lighter weight) but creates a more rigid structure. The Sea Gods CX iSUPs will be more rigid on the water than their ULF counterparts. The CX and ULF versions of each board also have different artwork (except for the Ketos).