Comments on materials:

The surface deadening material.  There are several  materials out on the market that claim to reduce noise transmitted through surfaces.  A typical situation would be a firewall - less engine noise passed through to the passenger compartment.   Most of these products are the same thing.  A thick sheet of plastic /rubber /  asphaltic material with an adhesive on one side.    It is about 2-3mm thick. 

The material is bonded to one side of the metal, and deadens the vibrations of the metal.  One manufacturer claims that the energy of the vibrations (the sound) is converted into heat.   This makes sense, as the energy has to go somewhere.  To the passengers in the car, the noise has to come through the firewall, which means the firewall picks up the vibrations from the engine, and vibrates in harmony with the noise.  Thus the noise is transmitted through the metal.  The problem with these materials is their effectiveness.  One manufacturer (I won't say who) went so far as to post 'scientific results' of their product's effectiveness on their website.  It's all very impressive, with charts and decibel measurements and other such eyewash.  But the information presented is rather a telling condemnation of its own product.  The efficacy of the material is inversely related to its temperature.  The higher the efficacy, the lower the temperature.  Restated, the warmer the material, the less effective it becomes.  The efficacy of the material drops by 50% in the temperature range from 0°C to 30°C.  Now, think for a minute.  How much time is your engine firewall at 0°C ?  at 30°C?   30°C is a lot closer to 'normal operating conditions' than  0°C.   So, this wonderful (and expensive) material is only half as effective at its job under  'normal conditions' as under freezing conditions.  That's rather disappointing from a materials-science standpoint.  So, my recommendations?  Some sort of material that is adhered to the metal is useful, but don't waste your money.   You want to limit the vibrations of the metal.  I suspect there are a number of substances out there that will accomplish this goal.  Some of these materials are purposely marketed for automotive applications (and are thus expensive) others are not.  Do some homework, and don't pay a lot of money for frivolous science.

The noise absorbtion material:  This stuff is made of shredded textiles, bonded together with some type of light adhesive.  It looks as though is made of shredded cloth, mixed with water & adhesive to form a slurry, molded into sheets, and dried.  The textile fibers are intertwined in a mass that is about 2cm thick.   It is much less expensive than the other material.  This photo is of the fiber side of the material.  I have torn one side as part of trimming it, and I am binding the edge with duct tape.

On one side of the textile sheet is a thin layer of reflective material (aluminum?)  The reflective material is to reflect radiant heat.   Here is my only close-up of the that side, where I am trimming a sheet to fit next to the heater pipes.

I was working with this stuff on a sunny day, and it definitely reflects heat

Since I had both materials, I decided to install one layer of each on the firewall.

First, I gave the firewall a good scrub with engine degreaser

Before	After

Then a layer of rust-proofing primer and paint.   The label on the paint can said "silver" which looked pretty close under the mercury- halide lamps of Home Depot.  It turned out to be a little more bright than what I was hoping for.

Tools I used:

Set the sheet of rubber / asphaltic material out in the sun where it will absorb some heat and soften.  It will be easier to handle.

The brown paper will become a template for the asphaltic material. Cut a section that is a bit larger than the area you want to cover and then press it onto that area.

Make sure the paper covers all of the steel, including up & underneath the 'shelf' for the windshield wiper.

Mark the front edge with a marker

Trim the paper along the line you marked.

Put the trimmed paper back in the car,

make sure it is all the way in & under the wiper shelf.  Now that it is smaller, it will be easier to manipulate and fit.

Mark it again.

and trim it again.

Put the side with your ink markings AGAINST the side that has the adhesive.

Trim the material.

And put the trimmed material into the area to be covered.

Mark the areas that need to be cut for a better fit.  Here, I am marking the place for the crosspiece that supports the 'shelf'.

Trim the material again. and also note the locations

You thought you were going to put the deadener in straight away, right? Wrong!!  Now you have  a very good template for trimming the second layer of insulation.  Put the deadener face up on top of the heat reflective material.

And trim it back.  The fibers of the material will leave a ragged edge where you have cut it.

Use duct tape to bind the edges.

Spray the adhesive on the firewall.  Even though the sound deadener has its own adhesive, I did not want the stuff delaminating in several years.  The adhesive is cheap, just use it.

Remove the plastic layer from the deadener, exposing the adhesive.

And install it.  Have your knife nearby, as you will need to make some cuts to get a better fit.

I used this roller to press the material to the steel.  This is a 'seam roller,' used to press down the seam between two sheets of wallpaper.

I made the rest of the panels for the firewall from the scraps of the first cut on the deadener.

The area are smaller, and you will need to punch holes to accommodate various bits.

I set screws wherever there were holes, so that they would not be filled up and hidden under the deadener.

The right side of the firewall after I installed the trimmings from the first section.  Note that I left the paint code disc exposed, and all the holes have bolts set in them.  With the asphaltic deadener, it is not necessary to cover 100% of the steel.  The value of the deadener comes from its ability to absorb the vibrations that would pass through the steel.  Larger surface areas of steel pick up harmonic vibrations more easily.

I set a  light to shine on the installed deadener.  The instructions recommended heating the material to make it adhere better.

The section of the heat reflective sound absorber fits reasonably well.

A little spot-trimming is necessary.

Spray the adhesive on the insulation.

And install it on top of the deadener.

For the section on the right side, I did not use adhesive, as I might have to pull that section free to access various bits.