What exactly happens...

What exactly happens when you infuse carbon fiber with vinyl ester? Why is it “not right”?

Most carbon fiber has a sizing which is not directly suitable for vinylester or polyester. This means there is less adhesion to the fiber, which can result in premature failure of the part.

That said, many parts are overengineered (if engineered at all) and not all parts are loaded (think overlays as an example)

Some suppliers (mostly multiaxial fabricators) offer carbon with polyester or ve suitable sizings, when requested.

(Hi Herman)

You are so right. I will edit the post, to prevent any confusion.