Acoustic insulation batts, which to buy?

Rockwool is the best batts for the job but is a glass material, so correct safety measures must be adhered. Unfortunately you cannot stop all noise as the flooring above is usually fixed to the same member as the ceiling.

While they are all made from the same material, acoustic batts are significantly more dense than a standard insulation batt. And more costly too.

We have Bradford soundscreen rockwool (the new version is high density glass wool Home ) R2.5 (88mm) between floors. While it does attenuate the sound levels somewhat it is not the total solution. It would depend what the upstairs is to be used for. Will it be carpeted? What sort of underlay will be used? What style of construction is used, chipboard, concrete, tissue paper.... Ours is chipboard flooring on 250mm posi-joists. With no carpet up stairs (at the moment) footfalls are still easily heard. A radio or TV at "normal" volume with any doors in between closed can only just be heard if you stand still and listen for it. There are a lot of things to take into consideration when sound "proofing" (reducing). De-coupling the floor, mass batts, flanking sound- up through wall cavities and through power- points and penetrations etc etc..... If you haven't laid the flooring already, you may want to consider something like Green tape to add to the total system. Foam Sealant Green Tape V494 » Foam Sealant
While on the subject of building an upstairs.... Make sure your design allows you enough room to run any services you need between floors. things like: electrical wiring, plumbing, heating and cooling ducts. (remember their dimensions are internal not external), smoke detector link wires, communications, cable, ethernet, phone, hot water controllers, alarm, heating and cooling zone controller wiring etc etc... If you miss any one of these it is a real nightmare to retro fit, especially if there is insulation in the way.

Thanks for the tips, the green tape sounds like a good idea to include.

New floor is going to be suspended above the existing ceiling, it will be lvl loists, with yellow tongue and t&g 19mm flooring. I'll plan to place in a few extra conduits for the forgotten cables....

Rockwool sounds like the go then, I would prefer not to use it as be all have asthma here. I know it has been proven to be safe but anything that is a respiratory irritant always worries me.

The new version of the Bradford Soundscreen bats are much nicer to use than the old one. They are much tighter bonded and less dusty. A simple dust mask for installation works well.