Best Sound Proofing

[reiner]

My sound proofing foam around the motor is falling apart and I need to replace it. I had a look at the Boat shop and they sell a foam with aluminium foil on the outside. The salesman said they only got the one with lead in it.
Firstly why does it have Lead in it? Secondly is it what I need?
Pricey too......about $100 for a piece 3ft by 4ft.
Has anybody come up with better and cheaper solutions?
Cheers
Reiner

[s/v Jedi]

Yes, the expensive stuff with the lead in it is the good stuff.

[MarkSF]

This was the best deal I could find :

Soundown Insulation Barrier 1X32X54 SDN-IVF1010MNSFT12 - Mufflers And Accessories - JMSOnline.net Marine Supply and Boating Store

Nonetheless, it cost about $300 to insulate the whole engine compartment if you include hardware, silver tape, spray adhesive, attachment pin kits, etc.

It is essentially mass that forms the sound barrier, the more mass the better, hence lead which is heavy. The above insulation uses lead-loaded vinyl.

Think of the barrier as forming a second wall to reflect and absorb sound. The foam is there to support the wall, and to space it.

[sailvayu]

The reason for the lead or most now use high density plastic is because it helps absorb and stop the sound waves. It is usually placed between 2 layers of foam allowing the dense material to harmlessly vibrate and take the energy out of the sound waves. The foil face is to block Vapors and fumes from breaking down the foam. using perforated metal sheeting has been shown to help as well but of course adds to the cost. Soundown is the best product now on the market.

[stillbuilding]

Are there not some paints that are applied to the wall before the above to enhance the insulation effect?