Carbon fiber has a high ultimate strength (the force required to break it) and a very high stiffness (the amount it stretches/bends when force is applied to it). Fiberglass, Kevlar, and carbon fiber have all got approximately the same strength and are stronger than aluminum or steel. Carbon fiber is far stiffer than aluminum, steel, fiberglass, and Kevlar. This makes carbon fiber ideal for making a strong, light, stiff structure and is why we use it.
The downside of carbon fiber is that it is brittle (has low fracture toughness). You can easily cut thin sheets or cloth with scissors. Carbon fiber cracks easily particularly in cases where the force is quickly applied (during impact loading such as a crash, it can shatter). Furthermore, once it cracks a bit, the crack can easily grow longer and a cracked structure (wings, fuselage) is not a good thing.
Kevlar on the other hand, has a particularly high fracture toughness. It is much harder to crack, very difficult to cut cleanly even with very sharp scissors, and stands up well to impact loads. That’s why it is used for bullet-proof vests, lightweight and strong kayaks and, now, pickleball paddles.
So, why are manufacturers moving toward Kevlar and, perhaps, away from raw carbon? Here are some general opinions.
Carbon is best suited for areas that require a higher stiffness and strength. While carbon fiber offers the best strength and rigidity to weight in the industry; it is also generally the most expensive of reinforcements (HMMM).
Carbon fiber is also much more straightforward to cut, sand and machine in comparison to Kevlar, which requires specially made drill bits once laminated.
That said, Kevlar offers a better abrasive strength than carbon fiber, which is why it commonly associated with bulletproof vests. What this means is that a Kevlar-faced paddle will last longer, be able to create more spin, and probably provide better control, but less power than carbon fiber paddles.
I have one Kevlar-faced paddle, a Pickleball Apes paddle. Body Helix will soon release a new paddle that is carbon-faced, and I cannot wait to get one. Some of you might know that Body Helix is already one of my favorite paddles.
This is an excellent article explaining the advantages of carbon fiber and Kevlar for pickleball paddles.
Here is my review of the Pickleball Apes paddles: https://theadventurousboomer.blog/pickleball-apes-paddles/