According to this calculation, if the average functionality of one reactant (𝑓 𝑏 ̅ , for example) is fixed, there will be a critical functionality of 𝑓 𝑎 ̅ . The reaction system has no risk to gel with the increase of component A if 𝑓 𝑎 ̅ is below the critical functionality, while gelation will occur with the increase of component A if 𝑓 𝑎 ̅ is higher than the critical functionality, and the gel point is the degree of reaction when 𝑓 𝑛𝑏 ̅̅̅̅ diverges to indefinitely large.