Please remember to quote the relevant rule in your question. VUR3 reads as follows, with a portion bolded for emphasis:
<VUR3> Teams are allowed to fabricate their own unique components for each of their Robots from the ollowing additional raw materials. These parts may be fabricated using techniques that may otherwise e prohibited in VRC, such as welding, brazing, casting, forging, hot/cold rolling, tempering, or gluing.
a. An unlimited amount of non-shattering plastic from the following list: polycarbonate, acetal monopolymer (Delrin), acetal copolymer (Acetron GP), POM (acetal), ABS, PEEK, PET, HDPE, LDPE, Nylon (all grades), Polypropylene, FEP.
b. An unlimited amount of silicone, polyurethane, or other rubber.
c. An unlimited amount of composite materials, such as G10 (Garolite), FR-4, or carbon fiber.
d. An unlimited number of plastic 3D printed parts.
e. An unlimited amount of steel, aluminum, brass & bronze.
The intent of <VUR3> is to encourage Teams to explore fabrication techniques like milling, 3D printing, injection molding, sheet metal punching, etc., to develop their own new robotic components in addition to the “standard” set of VEX components permitted by <VUR2> . To utilize these techniques, raw materials from the list provided in <VUR3> may be used.
However, the intent of <VUR3> is not to legalize all commercially available items made from these materials. The only commercial components (other than pneumatic components) that may be used are those purchased from VEX Robotics, as specified in <VUR2>. For example, aluminum billet may be used to machine a custom bracket. However, purchasing a custom aluminum bracket is not within the spirit of this rule. Similarly, pre-drilled or extruded metal, such as angle aluminum, is not permitted, unless it can be found on www.vexrobotics.com.
In the context of VUR3, commercially available "products" are not the same as commercially available "raw materials". Tubing, sheet, plate, etc are examples of commercially available carbon fiber raw material that could then be modified. Bike seats, wheels, drone chassis, spoilers, brackets, props, etc would be considered carbon fiber commercially available products that would not be legal for use.
To that end, creating a custom carbon fiber mold / layup for a unique VEX U part would be an example of a fabrication process that is permitted (and encouraged) via VUR3.
We would encourage teams to document their fabrication processes thoroughly for inclusion in the Engineering Notebooks, to avoid any concerns or suspicions regarding custom-fabricated vs commercially-purchased parts.
EDIT: This response was edited on June 1, 2020, to clarify that "angle" is not a permissible example of commercially available raw material that can be used.