Travel and trade between the islands that compose the Sea of Stars is primarily through starships and skyship some people (and groups) try to find other ways to move safely between the islands that is not reliant on rare woods or magic.
The dwarves in particular have sought our other methods of aerial travel to replace their expensive gemburners and crystal ships. While the Sen’tek seek to use ways to travel that the dragons will not sense. Others simply seek new innovations and the excitement of air travel.
Various sorts of hot air balloons and semi-rigid airship with lift provided by heated air have been tried but their limited carrying capacity and range have made them impractical for anything beside short range transportation but they are popular at fairs and for aerial surveys.
Use of gasses, such as hydrogen or helium, alchemically refined from natural gas (or other sources) has been tried but both the difficulty of refining and working with such gasses, combined with the flammability of hydrogen, have limited the ability to develop these technologies very far. Purely alchemical lifting gasses, such a purified air or elemental infused smoke, have had greater success but move into magic adjacent territory which is not the aim of all of the practitioners, but several of the dwarven holds have managed airships carried by such gasbags which are viable if ungainly forms of local air transport.
Notes: Image from the Wellcome Collection and used under a Creative Commons Attribution 4.0 International license.
Sea of Stars RPG Design Journal 