What's the difference between polyurethane finish and polyurethane plastic?

The **plastic version** is made by mixing two liquid chemicals (MDI & polyol) which react immediately and become a solid. **Polyurethane finish** is applied as a liquid and dries, no mixing involved. 


* Or are they not related at all?


Prompted by [Veritasium YouTube video](https://www.youtube.com/watch?v=DWkYRh6OXy8).


