Sizing is a surface treatment on the reinforcement fibers. Its compatibility with the proposed matrix belongs in the material review. Matching the carbon fiber name or tow size alone does not establish that two reinforcements are interchangeable in a particular resin system.
Start with the reinforcement product
Michelman describes sizing as a way to tailor reinforcement surface chemistry to the matrix resin. For an actual quotation, ask for the reinforcement product designation and the supplier’s stated matrix compatibility. A generic statement such as carbon suitable for composites leaves that interface undefined.
Keep it distinct from a finished coating
The sizing on a fiber is not the clear coating applied to a completed shell. A polished photograph therefore tells little about this material choice. Record the resin system and the identified reinforcement together, especially when reviewing a proposed substitute.
Make a change review specific
If the reinforcement source changes, ask whether the sizing or its designation changes too. The supplier should identify the basis for accepting the proposed combination. Do not infer finished-part strength from the sizing description. Sample and test evidence should refer to the construction actually supplied, so a useful material detail does not become an unsupported performance claim.
Further reading: Michelman: reinforcement sizing and resin compatibility.