Mail Balloons are small-scale airships commonly used by Delvers of the Abyss to transport letters and light packages to the surface from inside the hole. They can carry a reasonable amount of weight. There are two main types:
- The Gas Balloons are fueled with special floating seeds that are full of a gas lighter than air. The seeds are parasitic and infect bugs that eat them. They don't lose air over time, so they will not stop floating until they reach the edge of the Abyss. The seeds are sensitive to the atmosphere and will not float past this area. As a result, they stop near Orth for easy retrieval. The greatest disadvantage of these balloons is that the seeds are often consumed by large birds and insects that are attracted by its scent. Delvers often use a bird repellent to keep them away from it, but it doesn't always work. Currently, these are most commonly used.
- Hot Air Balloons are an older type that isn't seen very often nowadays. The balloon ascends using a fire that heats the air within the balloon. These work fairly well for short distances but the fire sometimes goes out midway, and other times it ends up floating in the sky beyond Orth. Additionally, delvers must bring the heavy fuel with them as the descend into the Abyss. It has the advantage that it often goes unnoticed by the local fauna of the Abyss.