I've been reading about masks and the consensus is that there is no real consensus.
The difficulty seems to be not with the mask's properties as an effective barrier but with its fitting. Many people you see wearing masks have great gaping gaps round the side and top and to all intents and purposes they might just as well not wear them. In fact in those circumstance the mask is more likely to protect others from the user rather than the other way round.
Whilst on the subject, it's worth considering a little about the physical size of the virus. Covid-19 is one of the larger viruses. It is about twice the size of a common influenza virus. That said, if a human hair was expanded so that its diameter was the width of a football pitch, on the same scale the virus would occupy about ten centimetres - about half the size of the penalty spot. This means that around seven or eight hundred viruses would, side by side, measure the width of a human hair.
It has to be a pretty good and well fitted mask that will trap such tiny particles with any degree of certainty.