tight barriers are crucial for animals. insect respiratory cells establish barriers through their extracellular matrices. These chitinous-matrices must be soft and flexible to provide ventilation, but also tight enough to allow oxygen flow and protection against dehydration, infections, and environmental stresses. However, genes that control soft, flexible chitin-matrices are poorly known. We investigated the genes of the chitinolytic glycosylhydrolase-family 18 in the tracheal system of Drosophila melanogaster. Our findings show that five chitinases and three chitinase-like genes organize the tracheal chitin-cuticles. Most of the chitinases degrade chitin from airway lumina to enable oxygen delivery. They further improve chitin-cuticles to enhance tube stability and integrity against stresses. Unexpectedly, some chitinases also support chitin assembly to expand the tube lumen properly. Moreover, Chitinase2 plays a decisive role in the chitin-cuticle formation that establishes taenidial folds to support tube stability. Chitinase2 is apically enriched on the surface of tracheal cells, where it controls the chitin-matrix architecture independently of other known cuticular proteins or chitinases. We suppose that the principle mechanisms of chitin-cuticle assembly and degradation require a set of critical glycosylhydrolases for flexible and not-flexible cuticles. The same glycosylhydrolases support thick laminar cuticle formation and are evolutionarily conserved among arthropods. Oxygen uptake is vital for all animals and an essential factor responsible for the limitation of fitness 1. Arthropods, especially insects, actively perform tracheal ventilation and diffusion to oxygenate their organs 2. The tracheal system is a hallmark of insects limiting their sizes, even in terms of giant evolutionary insects when hyperoxia occurred during the late Carboniferous and early Permian 3. The Drosophila respiratory system consists of multicellular and unicellular tubes. They together form a complex airway network that transfers oxygen to target tissues 4,5. Oxygen transport requires barriers to multicellular tracheal tubes. The intercellular diffusion barriers form at the lateral membrane by tight junctions analogous septate junctions (SJs), which prevent the paracellular flow of fluids across the tracheal epithelium into the lumina of the airways 6,7. Chitin-containing cuticles establish extracellular barriers against infections and to withstand tension forces 8,9. These include hydrophobic layers facing the lumen, which are impermeable to in-and outflux of fluids 10. Importantly, tracheal chitin-cuticles assemble to assist tube maturation and partially degrade in subsequent steps to support airway clearance during late embryogenesis 11. A crucial but less understood aspect is how the assembly and degradation of chitin-cuticles can occur 12 while maintaining protective barriers and integrity of the tubular system. Tracheal branching is genetically highly controlled and often evolutionarily conserved 13-17. After initial branc...