The crystalline sponge method facilitates the X-ray structure determination of samples that do not crystallize or are too sparsely available to afford viable crystallization. By including these materials in a metal–organic framework, the structure of the guest molecules can be determined. Some of the inherent difficulties of this method are discussed and the use of Cu Kβ radiation is presented as a simple and effective means to improve the quality of the diffraction data that can be obtained from a sponge crystal.