Fabric of Reality is a block from the Dimensional Doors mod. It is the same color as the void; to the player, the two are indistinguishable. Fabric of Reality can be found in Pocket Dimensions in a cube surrounding the dimension, and in large stacks in the chests of Dimensional Dungeons.
The player can easily break Fabric of Reality blocks with their hand, but the block will not be dropped. If the player attempts to place a block on a piece of Fabric of Reality, the block will replace the Fabric of Reality. The player can place blocks on top by sneaking, then placing the block.
The block also emits a decently bright light level, enough to not let enemies spawn inside a pocket dimension, granted there are no other blocks blocking the light.
It has been known that these devilish blocks have been used to confuse players into falling into traps within the chain of Dimensional Dungeons.