A few weeks ago I was surprised to discover that my car’s engine was getting louder. Rather than being a fault, it turned out that the hood insulation was wearing away, meaning I had to replace it.
Luckily the process is quite simple and there are several different products that can achieve great results. In this article, I’ll talk you through my DIY under hood insulation guide, along with my recommendations for the best products.
Why do I need under hood insulation?
Not all cars are fitted with under hood insulation when they leave the factory, but some are. The easiest way to check whether your car has under hood insulation is to simply lift the hood. If there’s a layer of anything from foam to fabric on the inside, then you have hood insulation.
But why do you need hood insulation anyway? Insulation under a car hood can be for either thermal or sound insulation, although most products offer both. You might think that your car doesn’t need acoustic insulation, but you’d be surprised at how much difference it makes.
Much of the noise pollution in a car is caused by vibrations. There are many reasons why your car might be vibrating, although you can always expect some. After all, a car has many moving parts, which result in a level of wasted energy.
However, the real issue arises when these vibrations transfer into the car’s body, which can lead to excess noise pollution inside the cabin. Luckily this is something that under hood insulation can combat quite effectively.
Similarly, thermal insulation inside the hood has a number of uses. On a superficial level, it helps to preserve the paint on your hood from heat damage. While this isn’t at the front of everyone’s minds, it does help to save a bit of money.
Another reason not many people think about is that it can be helpful if your car catches fire. Thermally insulating the hood can give you a few extra seconds to get out of the care in the event of an engine fire.
So thermal and acoustic insulation under a car’s hood actually has a number of uses. What’s more, the materials are fairly inexpensive and easy to install, so there’s very little reason why you shouldn’t fit them in your car.
What materials can you use to insulate your car’s hood?
When it comes to insulating a car’s hood you have 2 main options: sound deadening mats and hood liners. There’s realistically not much difference between the products, other than what insulation they prioritize.
For example, sound deadening mats, as the name implies, focus on acoustic insulation but have a level of thermal insulation. Hood liners, on the other hand, focus on thermal insulation. They may or may not have acoustic insulation depending on the brand.
The main buying criteria for choosing the right product include:
- Thickness. A thicker mat will provide better acoustic insulation than a thinner mat.
- Ease of use. Many hood insulation materials have a self-adhesive backing, making them very easy to install.
- Cost. Generally speaking, price does have an impact on quality, but there are some budget options that do an amazing job.
- Mass. As with thickness, a mat with more mass is going to do a better job of insulating. However, a mass-heavy mat doesn’t necessarily need to be thick.
- How much you need. Some brands offer their products in sheets, and others in rolls. Which you choose will depend on how much product you need.
Obviously these buying criteria are only a starting point, but you can use them to choose the best product for your needs. While you can go with a single option, you can also consider combining several for the best results.
1. Sound deadening mats
Sound deadening mats are the best choice if you’re looking primarily for acoustic insulation. They’re a really effective product that’s designed with soundproofing in mind.
Most sound deadening mats use mass loaded vinyl or a similar product. This is what’s known as limp mass, which means it’s not only heavy but it also doesn’t vibrate when hit by sound waves.
If they don’t use mass loaded vinyl, then the product might use dense foam as its base. While this does the job fine, I’d recommend choosing mass loaded vinyl if you can, as this is the more effective product.
What’s more, many sound deadening mats have a layer of aluminum foil on the engine-facing side. This provides a level of thermal insulation by reflecting the heat away from the product, meaning you get the best of both worlds.
Dynamat (Amazon link) is always a good brand to go with when looking into hood insulation. They offer a number of different products depending on which part of the car you’re insulating.
The mats are made from high-density foam with an aluminum front and self-adhesive backing, making them really easy to use. This product comes in sheets rather than a roll, which means it’s fairly easy to work with.
Another good option for sound deadening mats is Hushmat (Amazon link). These mats are made from mass loaded vinyl and again have a foil front, so they provide both acoustic and thermal insulation.
The product claims to reduce heat loss by up to 40%, which is fairly impressive, and it offers sound deadening benefits to match. This product is slightly more expensive than Dynamat, but it’s probably the better of the 2.
2. Hood liner
As mentioned, hood liners generally favor thermal insulation over acoustic but often provide both through their choice of materials. Most will be made from foam rather than mass loaded vinyl, but still offer acoustic benefits.
Similarly, most hood liners will come in sheets rather than a roll, which does make them easier to work with. They also have a self-adhesive backing so are really simple to fit in your car.
Dynamat (Amazon link) is also a good choice when it comes to hood liners, but the product is made slightly differently to their sound deadening mats. This particular option is ¾ inch thick, meaning it provides good thermal insulation.
The foam provides primarily thermal insulation but does offer some acoustic insulation. The aluminum sheet reflects up to 97% of the heat away from the hood, which is fairly impressive.
Uxcell (Amazon link) is a good choice for hood liners that provide both thermal and acoustic insulation. This product is made from fiberglass cloth, which is fairly effective at insulating the hood.
This particular product can be used on all areas of the car but is still suitable for under the hood. It’s completely waterproof and reflects a large amount of heat away from the hood. What’s more, it’s really easy to use because it’s fairly thin and not as heavy as some others.
Combining hood liners and sound deadening mats
Although many products offer both thermal and acoustic insulation, arguably the best way to get the benefits of both is to use both. Doing so is really easy because most products are self-adhesive, meaning you can stick one over the other.
I’ll go through the method in more detail below, but if you choose to use both products then you simply need to repeat the method twice. Obviously use the sound deadening mat as the base and then add a hood liner on top.
It almost goes without saying, but always ensure any materials you put under the hood are fire retardant. After all, the last thing you want is for your DIY insulation to cause a fire.
DIY hood insulation method
Now that we’ve taken a look at the materials available we can look at the method for installing them. While it’s really not difficult at all, you have to take care when fitting them, as the self-adhesive backing will be ruined if you have to peel it off and start again.
The process is fairly similar to hanging wallpaper in principle: it’s all about the preparation and you basically only get one shot at application. If you’re concerned about this, consider practicing on some scrap materials first.
- Sound deadening mat or hood liner
- Sharp craft knife or large scissors (e.g. tailoring shears)
- Mat roller (Amazon link)
Note that the mat roller is optional, but it makes a difference to the ease of application. If you don’t want to buy one, you could always consider a paintbrush or wallpaper smoother instead.
How to fit the under hood insulation
The steps for actually fitting the insulation itself are fairly easy, but you should spend some time preparing the area first to ensure you get the best results. As previously mentioned, you only really get one shot at sticking it down.
1. Prepping the area
Begin by peeling off any existing hood insulation. Your hood might not have any fitted, but you’ll know if it does. Regardless of whether this is worn or not, you’ll need to remove it first.
It should peel off easily, but if not, then use a flat-bladed knife to gently ease it up at the corners, peeling the rest off by hand. Try to use as few tools as possible so you don’t damage the paintwork.
Next, clean any dirt and grime off the hood, as this will prevent the insulation from sticking properly. Depending on how dirty things are, you might need to use some degreaser (Amazon link) to remove any oil buildup under the hood.
2. Get your insulation ready
Start by laying a tarp or dustsheet down on your cutting area in order to keep the product as clean as possible while you measure and cut. You don’t want to get any dirt or debris on the sticky surface, so keep everything tidy.
If you’ve bought hood insulation in sheets, then you can really just stick these in and cut to shape. However, I’d definitely recommend measuring and cutting before you start the application so you get the best fit.
Cutting to shape also allows you to take into account any contours in the hood. Measure the size of your hood, and then split it into different pieces depending on any dips or rises, or to factor in things like air vents.
Another good option is to use your old hood insulation as a template. Lay it on top of your new material and draw around it. Then simply cut to shape.
3. Stick it down
Once you have pieces of insulation cut to the correct size, you can peel the backing off the adhesive side. Stick it down on one side and then smooth it flat. For example, start by sticking the top down and then smooth towards the bottom edge.
Alternatively, you can use the roller for this. It’s not a necessary tool, but it does help to stick things down firmly enough. After all, you need the best bond possible between the hood and the insulation.
If you mess up sticking a piece down, I’d recommend cutting a new piece and starting again. This is purely because the adhesive backing will lose enough stick for it to not be worth trying again.
4. Tidy it up
Once you’re happy with how everything is stuck down, you can trim off any overlaps with a sharp knife. Remember, though, you don’t want any significant gaps between the pieces, as this will allow sound and heat to escape.
As mentioned, if you want to apply multiple layers, simply repeat the process (excluding the cleaning and prep stage). If you need more information, this video shows the steps listed above.
Under Bonnet Hood Insulation to Replicate a Factory Look
Some final thoughts
DIY under hood insulation is a fairly easy process. However, what is complicated is choosing the right materials for your needs, as this will depend on whether you want to prioritize thermal or acoustic insulation.
Also consider the fact that if you want optimum acoustic insulation inside your car’s cabin, you should insulate this too. The process is exactly the same but the products are a bit different. That said, hopefully insulating your hood will give you enough experience to do the rest of the vehicle.