On Wed, 27 May 2020 14:47:03 GMT, John wrote:

I think I need a new one - but it got me thinking - is there an optimum
bristle length - and why?

I think this could make a good doctoral thesis subject.

What are wanting to sweep up?
What surface are you trying to sweep?

Inside on smooth vynl tiles and fine dry dust a 2 to 3" long soft
bristol works well. Same length stiff bristles don't but outside with
saw dust on ridged concrete (as left by the tamper to provide a
little bit of grip) the stiff bristle brush does super job.

--
Cheers
Dave.