advanced mechanical metamaterials with unusual thermal expansion properties represent an area of growing interest, due to their promising potential for use in a broad range of areas. in spite of previous work on metamaterials with large or ultralow coefficient of thermal expansion (cte), achieving a broad range of cte values with access to large thermally induced dimensional changes in structures with high filling ratios remains a key challenge. here, design concepts and fabrication strategies for a kirigami‐inspired class of 2d hierarchical metamaterials that can effectively convert the thermal mismatch between two closely packed constituent materials into giant levels of biaxial/uniaxial thermal expansion/shrinkage are presented. at large filling ratios (>50%), these systems offer not only unprecedented negative and positive biaxial cte (i.e., −5950 and 10 710 ppm k−1), but also large biaxial thermal expansion properties (e.g., > 21% for 20 k temperature increase). theoretical modeling of thermal deformations provides a clear understanding of the microstructure–property relationships and serves as a basis for design choices for desired cte values. an ashby plot of the cte versus density serves as a quantitative comparison of the hierarchical metamaterials presented here to previously reported systems, indicating the capability for substantially enlarging the accessible range of cte.
