Exposed Carbon Fiber Body Panels Are Failing Spectacularly And Costing Owners Thousands

There was a time there in the 2000s when carbon fiber was the hottest thing, aesthetically speaking. People (and automakers) were installing on their cars expensive carbon fiber hoods, trunk lids, spoilers, mirrors, and on and on. Even interiors were being bathed in a sea of tiny gray and black zigzags — some real, some fake. Sadly, it only took owners a few years to realize that, as cool as carbon fiber may look, the real stuff can be a humongous liability if it’s exposed to sunlight.

One of the wildest Reddit posts I’ve seen in some time has a title that begins with “So… part of my roof flew away.” Come again? What?! Your roof flew away?

Just look at this:

So… part of my roof flew away. Anyone else with a fading or delaminating roof ?
byu/SloMoShun inBMWi3

If that Reddit embed isn’t working, behold the images of a really messed up BMW i3 roof:

It never ceases to amaze me just how many ways automobiles can fail. Between all the sensors and computers and complex mechanicals found in internal combustion engine vehicles (have you seen the inside of a valve body?), the world has enough silly ways for a car to break. Heck, BMW somehow managed to build engines whose rod bearings are basically a standard maintenance item.

Now we have to worry about our roofs failing? Sadly, if you own a carbon fiber-roofed car like I do, the answer is yes.

That BMW i3 roof that someone with username SloMoShun posted to Reddit shows the top layer of resin having completely fallen off the vehicle. Here’s how it should look (this is my own BMW i3):

This is a widespread issue. Look at how bad this other BMW i3 — posted by YouTuber “How_RV_going to do it” — got:

And this BMW M4 isn’t great, either:

This E92 M3 looks awful, as well:

And it’s not just BMW; look at how bad one of the carbon fiber side “blades” looks on this Audi R8:

San Diego-based 2M Autoworks — a well-known BMW tuner — explains the situation a bit on its website, writing:

Many of the M models of BMWs such as the M3, M4, M5, and M6 come with a carbon fiber roof straight from the factory. This carbon fiber roof looks awesome [and] also shaves some weight from the car and lowers its center of gravity. However, this roof is prone to problems over time.

These roofs are notorious for peeling, yellowing, and oxidizing which can ruin the look of your vehicle. Often this may be a result of poor maintenance on the roof when the owner fails to wash and wax it as often as they should. However, even the most maintained BMW carbon fiber roof may start to peel. Just like regular paint and headlights carbon fiber is still prone to oxidation. As the clear coat on the roof starts to degrade and the carbon fiber underneath essentially starts to rot. Unfortunately, no amount of polishing and wax can save the roof once this process has begun.

BMW does say they cover the carbon fiber roof under warranty on some newer vehicles. However, if you look online, you will see many people complaining that the BMW dealership refuses to repair these damaged carbon fiber roofs. They will often say it is a result of rock chips or other debris hitting the car and is no longer covered.

When the resin weakens due to UV exposure, it can no longer effectively hold the carbon fibers in place, potentially leading to delamination or the separation of layers. 

Even though car people often just use the term “carbon fiber,” the full term is CFRP — carbon fiber reinforced plastic. It’s a combination of woven polymers (carbon fiber) and a thermosetting plastic (resin). The issue, as I understand it, is that heat and especially UV radiation damages the resin, and once that’s compromised — and especially if moisture gets under it — the carbon fiber unwinds or “delaminates.”

Protech Composites, a Vancouver, WA-based carbon fiber vendor, has an entire article about carbon fiber UV stability appropriately titled “Is Carbon Fiber UV Stable? What You Need to Know.” Here’s what Protech Composites says about this issue, starting by describing how carbon fiber is made, and why resin is needed in the first place:

How Is Carbon Fiber Made?
All carbon fiber suppliers start the manufacturing process in the same basic way. Carbon fiber panels, fabric, sheets, and all other products are made from a collection of carbon fiber strands that are thinner than a human hair.

These fibers are made from a polymer precursor material known as PAN (which stands for polyacrylonitrile and contains carbon). This is a plastic that is spun into very fine fibers, then washed and stretched to a very fine diameter that helps to ensure that the carbon fiber crystals it contains are very tightly bonded.

These fibers are then heated in an oxygen-controlled environment, which adds oxygen to the fibers, changing the bonding structure from linear to ladder-shaped. This is known as a cross-linked polymer, and this form of bonding is one of the reasons that gives carbon fiber such high strength, high flexibility, and overall high performance.

After this, the fibers are heated again, this time in an oxygen-free environment that forces all of the impurities from the matrix, leading pure carbon fiber behind. After this process, all that remains are tightly-linked carbon crystals that are exceptionally lightweight and strong.

These carbon fibers can then be wound into collections called Tows before being woven into sheets. The next step is where the issue with UV light arises.

These pure carbon fibers themselves are not only UV stable; they are effectively UV-impervious. So, in one sense, to answer the question “is carbon fiber itself UV-stable?” the answer is yes.

However, after being woven into sheets or panels, the next step in the process is to add epoxy resin.

Why Do Carbon Fiber Suppliers Add Epoxy Resin to the Carbon Fiber Matrix?

Carbon fiber manufacturers add epoxy resin to carbon fiber sheets and panels for several reasons. One is that epoxy resin is one of the few materials that will both penetrate and adhere to carbon fiber.

Another is that epoxy resin makes carbon fiber stronger. It reinforces the weave with dimensional stability when stresses, such as compression, torsion, or shear forces are applied. It also fixes the fibers in a specific geometric arrangement. This prevents misplacement of the fiber tows that can weaken the matrix.

Another reason is aesthetics. Because the resin fixes the fibers in place, it prevents a cosmetic disruption of the weave. The epoxy resin is also responsible for the high-gloss finish of many carbon fiber products. Unfortunately, some epoxy resins are not UV-resistant.

Then the company goes into the UV issue:

What Dangers Does UV Light Pose?

Ultraviolet, or UV light, is a form of electromagnetic radiation with wavelengths just beneath those of the visible spectrum. It is comprised of three main types: UVA, UVB, and UVC light, in order of descending wavelength, from 400nm to 100nm.

UVC light is the most damaging of these wavelengths and causes irreparable cell damage. This is also the wavelength that is responsible for most damage to certain other organic materials. For example, UV light can cause damage to certain synthetic polymers, such as PVC and certain rubbers. They become discolored and brittle with UV exposure and can even crack or crumble. This is known as UV degradation and it is a real challenge for synthetic materials producers.

UV light can also damage the epoxy that binds carbon fiber products. With prolonged exposure to UV radiation, the chains of polymers within the epoxy will break down, causing yellowing, fading, cracking, and crumbling.

While the UV light does not destroy the carbon fibers themselves, it can cause the premature degradation of sheets and panels by degrading their epoxy resin. In this respect, not all carbon fiber products are UV stable.

And here’s a bit about what you can do to not only prevent carbon fiber yellowing/fading, but also how to fix it once the damage is already underway:

What Can Be Done About It?

Luckily, many carbon fiber suppliers use UV-resistant epoxy resin to finish their carbon fiber products.

We use a vacuum infusion process to inject the carbon fiber with UV-stabilized epoxy with a low density and high compressive strength. This actually strengthens the carbon fiber composite matrix without adding very much weight. It also gives it an added layer of resistance to UV radiation.

For these reasons, products that are made with UV-resistant carbon fiber are suitable in many of the following industries in which exposure to sunlight is inevitable:

• Aerospace and engineering
• Automotive parts and accessories
• Marine parts
• Sporting goods and accessories
• Medical equipment
• Robotics and manufacturing
• Consumer goods, including knives and other products for outdoorsmen

Fading, yellowing, and cloudiness are common signs of UV damage, and to some degree, with enough exposure to the elements, all carbon fiber will experience some UV damage.

Whether your carbon fiber is made with UV-stable epoxy resin or not, it may be possible to restore it.

If your carbon fiber has no cracks and is only slightly yellowed or faded, you may be able to sand off the damaged epoxy and re-apply a fresh clear coat.

Use only very high grit sandpaper to prevent removing excess stock. Sand very lightly, and pay attention to the color of the dust; epoxy dust will be brownish, white, or yellowish. If it’s gray or black, stop immediately. This means you’re sanding too deep and are damaging the carbon fiber.

Once you’ve removed the layer of epoxy that was damaged by UV, apply a new clear coat finish to restore its high-gloss appearance.

The danger, though, is that epoxy resin being damaged, and the owner not having it repaired. Raw carbon fiber exposed to the elements can be damaged in such a way that it can be permanently damaged.

Since my BMW i3’s lid is still in good shape, I had to decide between adding a layer of UV-resistant clearcoat, painting my roof, wrapping it, or installing PPF; since I like the look of my carbon fiber roof, and since The Autopian is partners with XPEL, I decided to have PPF installed. Even with that, I’ll be watching my roof like a hawk, because 2M Autoworks charges $1,800 just to fix the resin assuming you catch that before it fails completely and lets the elements get into contact with the carbon fibers themself. And if you don’t catch it in time, well, just look at that damage shown in the first image in this article! Yikes!

Top Screenshot: YouTube/“How_RV_going to do it”