Underread_east is right, to protect you hearing you should be asking your company to provide suitable PPE. If you don't wear it you will substantially weaken your chances of making a claim should that become necessary.
Having said that, look up the attenuation data for the supplied Peltors, find some in ear plugs that equal or exceed that attenuation, and present the data to your H&S department.
Ear defenders ( like all PPE ) need to be worn to be effective.