Originally Posted by willhollin
Rockwool would work well.
There are purpose made products for this sort of application but seeing as you can get Rockwool pretty cheap it would seem stupid not to use it.
Just make sure you are not interfering with any ventilation. Oh, I doubt you will be able to pull it through from one side to the other as it will just pull apart. Looks like a floor up or ceiling down job.
Floor up would be the easy option. Are you sure the down lights have the protective cover? Most sparks (I was one for 17 years) would buy the cheaper option and tell you they fitted the best of the best