There are many links which I don't have to hand, I'll try and post some later but a search of Prof Carl Heneghan should pull up the clips of his evidence to the Oireachtas committee.
I've posted a link to the full transcription of that session above, you can quote the pertinent sections.
Prof. Staines challenged Prof. Heneghan's authority to speak on the subject give his lack of experience...
One of Professor Heneghan’s colleagues, Professor Trisha Greenhalgh, has conducted a systematic review of the evidence for masks. Unlike Professor Heneghan, I make my living analysing and interpreting observational data. I am extremely familiar with what one can and cannot usefully do with it in public health. I am moderately convinced by the evidence.
The evidence that masks protect a person from infection, particularly this type of mask or the cloth masks some members are wearing, is very low but the evidence that they reduce spread from an infected person is much better.
Prof. Kearney added:
I was a mask-sceptic at the outset of this based on the evidence that I was familiar with. However, like Professor Staines, I have looked at where they have been used at a population level. I have been convinced that it is part of the suites of things we need to do to address the virus.