Gummi Blocks are a material used primarily in the creation and modification of Gummi Ships. They are elastic and rubber-like in texture, and appear in many varieties. Each type has its own shape and properties and a wide variety of uses.
 Kingdom Hearts Birth by Sleep
In Kingdom Hearts Birth by Sleep, the Gummi Blocks have a larger part in the game's plot. They are known as Star Shards; King Mickey uses one piece to travel the worlds. The Star Shards also appear as star-shaped crystals, as opposed to the block-like, geometric shapes of typical Gummi Blocks. If the user does not know how to control the shard, it activates its power randomly and the traveler never knows where he will land or when he will be transported away; thus, Mickey's visits to the same worlds that Terra, Ventus, and Aqua end up are often purely coincidental. It is known that King Mickey is not the only character to come in contact with or use the Star Shard; both Ventus and Captain Hook have been shown to find King Mickey's Star Shard, and Donald Duck and Goofy use it to travel to The World That Never Was to aid Lea, Mickey and Riku against Master Xehanort.
 Kingdom Hearts
According to the Ansem Reports found in Kingdom Hearts, Xehanort caused Gummi Blocks to appear in Radiant Garden for the first time, and was also the first to study them. By this time, the Disney Castle world had already made use of this material, as King Mickey appeared in Radiant Garden in a Gummi Ship soon after. Unknown to Xehanort, by opening the door to the heart of Radiant Garden, he also opened the gateway allowing his world to interact with others.
A basic understanding of what Gummi blocks are can be inferred from the Ansem Reports. It appears that when the door leading to a world's heart is opened, the wall that protects that world collapses. Gummi blocks then appear in said world, as in the case of Ansem's study of the meteors, suggesting that the blocks are remnants of the protective wall of the world. The nature and origin of Gummi blocks is what allows them to travel to other worlds.
As mentioned in the Ansem Reports, Gummi blocks are "elastic" and "bond easily" when combined, as evident when creating Gummi Ships. The blocks themselves are very numerous and come in all shapes and sizes with properties attached to each. When added to Gummi ships, they provide advantages such as improved armor, increased acceleration and greater firepower. In both versions of Kingdom Hearts, specialized Gummi blocks can be used for other advantages, such as warp travel in Kingdom Hearts.
 Obtaining Gummi Blocks
 Kingdom Hearts
The primary way that Sora obtains Gummi Blocks is by destroying enemy Gummi Ships and obtaining blocks or blueprints from their remnants. Rarer blocks, however, can be found in chests throughout the worlds and dropped from certain Heartless. Later on in Kingdom Hearts, they can be purchased from Cid who, in a nod to his affinity with Airships, is an expert in Gummi engineering. Cid resumes his former work with Gummi Ships when Sora finds a Navi-G Piece (ナビグミのかけら Nabi Gumi no Kakera ) in Deep Jungle and he later gives a full Navi-Gummi to Sora. An entire set of Gummi Blocks is also awarded as a prize for finding all of the 99 Puppies for Pongo and Perdita.
 Kingdom Hearts II
Unlike its predecessor, Kingdom Hearts II gummis can only be obtained within the Gummi Ship mini-game, or through purchase in the Gummi Ship editor. Rare gummis are awarded by completing special goals within Gummi Missions, or by destroying special enemies.
Notably, enemy ships in Kingdom Hearts II are not made of Gummi blocks, but are in fact actual ships.