Polymerizes chitin, a structural polymer of the cell wall and septum, by transferring the sugar moiety of UDP-GlcNAc to the non-reducing end of the growing chitin polymer. [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + UDP-N-acetyl-alpha-D-glucosamine = [(1->4)-N-acetyl-beta-D-glucosaminyl](n+1) + H(+) + UDP Abnormal capsular morphology: lower fiber density, decreases capsular diameter. Belongs to the chitin synthase family.