Bagging seed heads - what bags?

If the material cannot breathe I think you're likely to end up with some mould happening.

For peppers/chillies I use 5x7cm bags, they are just about right for a single flower. For tomatoes I use 17x23cm bags which are big enough to cover a whole truss. If the stems on the peppers are too short I use the tomato bags on a whole branch instead.