Exotic Substances are consumable items that are used to improve other equipment or characters temporarily. They can be found at events, be part of your Groups income, or can be synthesised by Scientist characters between events with their leftover Research Points. These items are great ways to boost your gear for a day, or for the duration of a difficult mission.
There are 3 types of Exotic Substances; Exotic Particles, Exotic Reagents and Exotic Biotics (One type for each of the 3 Science Specialisations in the game). Each type can be used by scientist characters to enhance certain classes of objects for a short duration. The lammies for these items will have removable stickers which can be stuck to other lammies to indicate a change in their properties.
Physreps for exotic substances might be a small test tube of mineral samples, vial of coloured liquid or a small containment vessel.