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
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 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”
A can of latex paint is less than $50 and will coat it for years.
I can never figure out why someone would spend all that money for carbon fiber, use it outdoors , and not paint it. Is there some reason you can’t have pigment in the epoxy like in fiberglass gel coat?
Well clearcoat paint jobs on cars seem like a bad idea too, so what do I know. I know getting a single stage paint job seems to have become very expensive.
Ugly ugly clearcoat.
Be sure to re-apply the sunscreen every couple hours.
BMW finding new and exciting ways to dissapoint their customers.
At this point (probably long ago actually) I’d take a Nissan over a BMW.
Because I am the owner of a time machine, funny joke from a twelve year old last Sunday, ” if you go over 88mph in this car I want to go back in time so I am not in it”
https://en.wikipedia.org/wiki/Weymann_Fabric_Bodies
BMW rod bearings are a suggested routine maintenance item?
Why is that no surprise at all to me?
More context is needed. SOME regular BMW engines are built very poorly and indeed, eat rod bearings (see: N47). A lot of the engines mentioned in the article David linked are very high performance, high revving M-sport engines that are closer to a race engine than a regular car engine, and in that case, doing rod bearings every 80,000 miles doesn’t sound so bad.
Many BMW engines, like the M54 and N5X engines do not have rod bearing issues and routinely run for many hundreds of thousands of miles without issue.
Can you name a single other manufacturer that has their own enthusiasts suggest rod bearings as a routine maintenance item?
There are countless LS, Coyote, and Hellcat engines out there. I have yet to find anybody in performance circles suggesting routine replacement of rod bearings without any symptoms of problems, unless you’re already in there working on something else.
BMW owners will do a lot of odd, expensive things without explaining why it’s worth that much more than something that just works instead.
Yeah, fiberglass can be woven to look good, but they always paint or gel coat it for some reason for over 75 years.
Yeah, I’ve been waiting for this to finally become an obvious problem or to discover that the industry figured out some magic solution for this long-known issue, but I guess it’s the one they always had: paint. Saves it from the ugly weave look, too, though I guess it makes it harder for someone to show off that they got the CF roof on their overweight luxobarge. I believe it was Confucius who posed the question: if you can’t think you’re impressing random dorks at a car show with exposed CF weave roof, does it even have a purpose?
When I ordered my M2, I was initially going to get it with the carbon roof – mostly just because I thought it looked cool, but I live in the desert, so I decided against it for this very reason. I don’t love having a sunroof, but it’s better than dealing with a delaminating carbon roof.
Hey, being cheap has paid off finally!
Seriously, tho, that is nasty and quite expensive.
That’s what uv does to exposed composites. The marine industry has a lot of fixes for that I’m sure aerospace does too but it might be the one time marine is cheaper.
Does anybody have the Haartz Corporation’s (it was Haartz Auto Fabric when I worked there 48 years ago) number? Time for some vinyl roofs.
I think they make flea collars now
Haha! I believe that was Hartz Mountain, not sure if there’s a connection.
From cars that fall apart due to oxidizing metal to cars that fall apart from oxidizing plastic: DT sure does have a type.
Let’s hope E.N.H.R.N. eats plenty of blueberries.
I work in composite R&D and this is a big problem that is a concern in aerospace as well.
That’s the reason 787’s are only moved around the factory at night before they get painted. Simply to avoid any minuscule amount of uv degradation.
The additives have an effective life which as these cars get older will rear its head more and more.
As the resins degrade, the composite can also start to absorb more moisture and cause other issues.
I was going to comment similarly: There’s a very good reason you don’t see unpainted CFRP on aircraft.
Also, any water ingress into the stackup will be a disaster.
Clearly the solution is piano black plastic roofs.
Or in Subaru’s case: Rugged Black Plastic™
And with a shape totally mismatched with the underlying structure.
Genuine Woodgrain Applique
On the other hand, an i3 convertible would probably be a pretty fun car. Maybe a floppy chassis M convertible isn’t so bad after all since the roof is removed from the factory?
This was a problem when the first carbon bike frames/ wheels came out. As cycling, famously mainly done outside, often on sunny days. It was the reason the whole carbon fiber frames/wheels expire myth is still a thing. Was basically solved with paint and/or the sacrifice outer layer. Haven’t heard of a frame deleming due to UV exposure since Lance. Except Time frames, Time frames still due this Don’t buy a Time frame.
I remember way back in the day when Trek came out with the “Y Bikes”, everyone (myself included) thought that the carbon frames were really cool… but I still bought the Gary Fisher version because it was aluminum and carbon fiber kinda scared me. I know that a lot of the early issues have been worked out, but I’ve still never purchased a carbon frame bike.
Yeah I saw a few of these fail on I3’s and M cars at my old job. The I3s were at least 10 grand and up to replace the roof, M cars usually more like 15k. Definitely want to wrap these. I suppose a UV resistant PPF is t bad either. Regardless yet another dumb unnecessary way for modern cars to fail.
Ironically, some of that self adhesive “carbon fiber” contact paper stuff you can buy at PepBoys would probably protect your real carbon fiber roof.
Pretty sure the GR Yaris, maybe the Corolla too, more or less did that from the factory.
Yikes indeed! Of note, Chevy puts very expensive UV inhibitor in the resin for their exposed CFRP, but I assume many others don’t because of the cost. Did BMW blow it off to save bucks? If so, shame on them.
Does Cadillac? Asking for, uh, a friend.
Yes, I believe they do. However, I did not do a detailed analysis, so I may be wrong, but if anyone wants to place a bet…
I guess I’ll find out if my splitter and spoiler start delaminating. Hopefully different sides of GM talk to each other.
From the C6 ZR1
VERY expensive! Gold pressed latinum goes for less. Morn should drink that shit instead.
Without inhibitors epoxy starts to yellow very quickly so all manufacturers will use inhibitors of some sort. Unfortunately the inhibitors have a lifespan and can only inhibit a finite amount of UV energy.
Annoyingly they can’t be reapplied like sunblock.
This is peak BMW insanity, especially given that exactly zero people who drive a BMW with a carbon fiber roof have ever noticed the impact on the car’s performance.
I hate glue and for good reason, when it goes bad it’s a massive PITA.
A friend started doing display design for a large national big-box retailer about 20 years ago. The first thing they told him was that he could never use glue.
Another thing to worry about now I guess.
My Lancer Evolution VIII MR’s spoiler had its clearcoat start to delaminate. It was replaced under recall, since it was an issue with the resin.
Personally I’ve not been a fan of exposed carbon. I think the properties are neat, but I don’t need the car to be shouting “LOOK AT MUH CARBON.”
I had my Spyder RS’s hood fully painted (not the stripe, whole thing) from the factory. All the other Weissach required exterior CF was XPEL Ultimate 10d. I know better. I don’t want to know what it would cost to get replacements in decades.