The Master Mold Creation Process

The Master Mold Creation Process

"In this special series written in collaboration with René at, I document the 1:1 CSL carbon diffuser.

I cover the entire ideation, development, master & negative mold production process along with my unboxing impressions, DIY fitment and professional fitment.

This entry covers the pre-production process including positive and negative mold creations."

The differentiation. 

All current CSL diffusers on the market are made by creating a negative mold of a CSL diffuser. 

This is good, but not perfect.

The negative molds have a limited capacity for production. After it is past its tolerances, another negative mold needs to be made by sourcing another Genuine CSL diffuser. The initial CSL diffuser most likely aged and warped.

Some molds were clearly made from an aftermarket part as is often the case with eBay & Alibaba suppliers.  

It is why many eBay & Alibaba diffusers do not fit well. The prices are low, the initial craftmanship is poor and the return on Investment is made by extending the lifetime of the negative mold beyond its normal lifespan. 

The master mold.

The master mold is called the "positive mold. It is an actual 1:1 replica of the Genuine BMW CSL diffuser from which the negative molds will be created. 


The milling process was executed over multiple days on a 3 and a 5 axis milling machine. 



The Master Mold gets a high gloss epoxy resin coating. Once it is applied, it is ready to make the negative mold. 

René uses UREOL® epoxy resin. It is optimally tailored to the requirements of carbon composite mold making. Its applications are in the temperature range up to 140°C, especially well suited for prepreg carbon manufacturing. 


Release agent. 

The negative molds themselves are made from pre-preg & autoclaved carbon fiber. It is from this mold that the CSL diffusers will be made from. 

As of June 2nd 2022, René has applied the 8x coats of release agent in preparation for the negative mold creation. 

The process takes over 4 hours of careful application. 

Further milling.

The positive master mold was then further CNC milled on the edges and brackets to prepare for the final laser cut. 

This process requires extreme precision and is a major component to the OEM fitment we aim for. 

You can see the precise milling in orange on the picture below. 

Negative Mold.

René created the 1st negative mold from pre-preg carbon fiber. This mold was used to create the actual production units.

The mold is further reinforced by adding carbon fiber plates to ensure the mold stays true during production and autoclave process.

The negative mold will now be finalized by applying the various layers of release agent needed to start production. 


Speeding up production.

René re-invested the initial revenue into further production capacity by developing a 2nd negative mold for production. 

Shout to René for supporting EuroConnex and investing in the future. 

Pre-Production Units

My Phoenix Yellow 1:1 CSL Carbon Diffuser with CSL matching 1x1 weave pre-preg carbon fiber is produced, painted and currently curing before shipment. 

There were lots of questions surrounding the paint line. The answer from René was this would be naturally dictated by the ridge.  


Up next: unboxing impressions and my recommandations on specs. 



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