Mentioning about Rubber material, everybody knows something about rubber or even rubber products ,they may know it to be softer more than plastic products for sure , that is right especially working on the use of dumbbells . 

  For dumbbells in gym exercises, rubber may works harder than other things because the users do exercise by more weight day by day ,most of the users in the gym clubs dropped it on the floors while they are not able to hold it anymore .so the rubber parts will be in a terrible damage if the quality is not good when it impacts the floors eventhough the clubs use mat to protect the floor .because the weight of dumbbell will be heavy from 30-50kgs . in such impact , the welding between the steels and the handle will be also in danger if still the rubber quality is okay .

  In addtion, gym clubs or homes are the important places must be enviormental as much as possible , so be sure not to use anything not enviormental , in gym clubs, they need about several decades of dumbbell for exercise , it will be a smell problem if the rubber material is not good , by the way ,,we never do it at all .