The Hollow Competition Kettlebell is produced according to the international standard. The Hollow Competition Kettlebell is constructed from a single cast without fillers. This creates better balance during lifts as most competition bells with welded bottoms and fillers can shift and rattle around with movement making it harder to complete your workout. If you see a competition style kettlebell without an opening in the bottom it is filled with sawdust and ball bearings or other fillers. These will unsettle over time and make the lift feel unbalanced.