Researchers at MIT have created a foam and wax material which can be 3D printed in a lattice structure. When heat is applied to the material it becomes soft, allowing it to fit inn tiny placed, but when the heat is removed the material become rigid, making it structurally sound. Researchers believe that such material could be used for the creation of shape shifting robots which can enter small areas, like rubble from an earthquake or tornado. More details on this material can be found here:

Below is an example of the material: