A respirator or mask is one of the most important piece of safety equipment when working with fibreglass.   You will need protection from simple dust through to potential cancer causing fibres and vapours, especially in some paint systems.   These items of safety equipment range from the simple paper mask, through to simple air supply units, which totally isolate you from the surrounding environment.   You should discuss the various options with your fibreglass supplier who will advise you on the availability for each particular use and workplace situation

Some respirators will not work when used over a beard or for that matter (designer) stubble.   If you are not clean shaven, then consider using a suited hood.

Amongst others the 3M Corporation have available some excellent breathing appliances.

A well-run building workplace can take the pressure off the safety equipment by providing a clean environment.   Keep rubbish off the floor.  Remove fibre trimmings immediately and make sure you have adequate ventilation.   Keeping a clean workplace will go a long way to keeping you healthier.   You will reduce fire risks and keep your insurance man happy.