Blueprints are build plans that allow players to save their facilities for future use and rebuild them in an instant later on. They are shared across save files, allowing the player to expedite construction in any playthrough once they have a blueprint saved.
Unlocking
Blueprints are unusable until the Mass Construction upgrade is researched. Initially, only small facilities (up to 150 buildings) can be saved as a blueprint. However, upgrading Mass Construction will increase the limit until eventually any number of buildings can be saved.
Notably, the Mass Construction upgrade also restricts what blueprints can be used, not just those that can be created. For example, if a player has saved a blueprint with 1000 buildings in it, then starts a new save file, they will not be able to construct that blueprint until they research Mass Construction up to the appropriate level.
Mechanics
Selecting Blueprint in the hotbar will bring up the Blueprint Library, which shows all saved blueprints and also allows the player to make new ones. From here, selecting Create New Blueprint (or pressing CTRL + C) will put the player into blueprint mode, where they can draw a selection box to select all the facilities they would like to be in the blueprint. Right-clicking on a facility that has been selected will deselect it.
Each blueprint has a title, thumbnail title, icon(s), and description.
Additionally, the proportions of the planetary grid where the blueprint is created versus where it is placed cannot be significantly different. For instance, creating a blueprint at a planet's pole then attempting to build it at the planet's equator will not work. Additionally, tropic lines interfere with blueprint construction in several ways: if the blueprint is on top of a tropic line when it is created, then it must be placed on the same tropic line; otherwise, if the blueprint was not on top of a tropic line when created, then it cannot be placed on a tropic line at all.