If it looks, swims and quacks like a duck [...]

If it looks, swims and quacks like a duck [...]

"In this new Special Series, I document my unboxing feature review, paint & body process and my impressions on the final quality and aesthetics of the CSL carbon trunk made by Karbonius Composites

The first entry in the series covers my unboxing impressions. Trunks are arguably the 2nd most complex body panels on a car after doors, and the CSL gets a little more complex than a standard trunk. Let's see how Karbonius created theirs."
- Matt

[...] it's a duck!

The CSL trunk might arguably be the signature design feature of the E46 M3 CSL, even above the snorkel and splitters of the CSL carbon bumper. It turned a corner on the design language at BMW M, making way for rounder shapes that would later become a part of Chris Bangle's hallmark designs. 

I find the integrated wingless, ducktail'ed trunk embodies this change the most.

The OEM composites. 

The E46 M3 CSL is no doubt a classic masterpiece - yet it was back then a call to the future of BMW M. It had many M features that we take for granted today: carbon roof, front bumper & diffuser, a composite trunk and the infamous CSL airbox.

BMW M still manufactures the CSL trunk as of 2023 (SKU: 41-00-7-895-884).  They are made in Italy by a composite manufacturer using Sheet Moulding Compound (SMC), a polyester containing glass fibers. 

The OEM trunk is still the barometer for fitment quality, but not for weight. It comes in at 11.5 kg / 25.4 lbs.

BMW M was still learning to manufacture carbon composites at scale back then. Technology has moved on since its introduction in 2000 and I think we can do better. 

The Karbonius composites. 

In late '21, Karbonius released their take on the CSL trunk design. It showed technical promises. It was a complete pre-preg construction coming in at 5.5 kg / 12.1 lbs, less than half the weight of the OEM product.

In Spring '22, I received a trunk and collaborated with Karbonius to offer a group buy for 25x spots. 

Complete carbon construction. 

Composite trunks are complex body panels: they are made from multiple sections and need to have precise cut outs to integrate electrical, safety and trim components. 

Most often, carbon replicas use fiberglass inner shells to cut material costs. Karbonius opted to make the trunk entirely from pre-preg & autoclaved carbon fiber, including the inner shell. 

They picked a larger 4x4 weave, I assume to better conform to the complex shapes of the trunk design. 


1:1 exterior shell. 

The Karbonius CSL exterior carbon fiber trunk was designed by using the OEM CSL trunk as the basis for its CNC machined aluminum, negative molds. The outcome is a 1:1 design replica that matches the signature ducktail aesthetics.

The outer shell was finished in white primer. You can also opt for a clear coated, naked carbon look. 

The exterior shell has the necessary cut outs for CSL license plate lights and OEM trunk badge. 

The horizontal line crossing the trunk is another key design feature of the OEM trunk that is retained. The cut outs for the key lock and lights are evidently there as well. 

A simplified interior.

Karbonius redesigned the interior shell with a simpler, more appealing design.The upper section of the inner shell makes without the OEM ribbing.

They wanted to showcase their signature carbon craftsmanship and create room for another M logo. 

The relief is designed to fit a BMW M badge. You can still fit a liner and the holes are there, but I don't see the point. 

The interior carbon fiber is clear coated for a durable and quality finish. You have the option between Matte or Gloss clear coat. 

The inner section of the key lock is also present and replicates the OEM design to re-use your current trunk locking mechanism and key lock. 
Holes to fit the CSL trunk liners are present, always with the rubber stoppers. 
The trunk also features threaded inserts to bolt to the hinges. 
Karbonius adds their authenticity stickers by the locking mechanism. 


The Karbonius trunk is light, the carbon work is proper and I like the simplified inner design. 

But the true test of quality comes later on. 

Up next: it gets ready for paint, and test fitted. 

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