Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
ATC Issue All Types
General None Reported / Taken
Human Factors; Environment - Non Weather Related
We were with ZZZ Center and I was having trouble understanding the Controller. I told him that he was coming in 3x5. The Controller proceeded to tell me that he had numerous complaints about being hard to understand and the reason was; that he was required to wear a mask while at work. I started thinking about this and realized that I was having trouble with other controllers throughout the country and never made the connection.  We never had an issue but the Controller had to repeat himself several times which seemed to clog the radio.Suggestion - Have the controllers not wear face masks that might make their transmission difficult to understand.
Air carrier Captain reported the ATC Center Controller was difficult to understand because the individual was wearing a required face mask.