Rockwool/rocksil slabs are the most effective stuff without breaking the bank.
Note: they don't block much sound, they dampen the wall so you don't get resonance and vibration in the wall, but it all depends on what you are trying to soundproof, if it's normal conversation the insulation slabs will make a big difference, if it's a drumkit or loud hi-fi, you've got bigger fish to fry than 'what to put inside the walls'
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local