Abstract: A sheet contains swelling clay and non-swelling clay and exhibits excellent water resistance in high-temperature environment. The swelling clay contains a first component and a second component with different structures. The non-swelling clay is clay in which ions of the first component and the second component are exchanged in a dispersion medium, and is clay that exhibits a non-swelling property by heating. The sheet includes the first component (Li-substituted swelling clay), the second component (Na-type montmorillonite or K-type montmorillonite), and optionally a third component (filler), that is optionally contained. When a total weight of all components is set to 100 wt %, a content of the first component is 25 wt % or more and 80 wt % or less, a content of the second component is 10 wt % or more and 50 wt % or less, and a content of the third component is 0 wt % or more and 80 wt % or less.

Abstract: A sheet and a sealing material based on clay and excellent in an electrical insulating property in a high-temperature environment. A sheet, containing: a first component as a main component; and a second component optionally, in which the first component is clay, a diameter change rate is 10% or less, as thermal dimensional stability, when a weight of the entire sheet is 100% by weight, a content of iron oxide is 6% by weight or less, the second component is a filling material, when the weight of the entire sheet is 100% by weight, a sum of the first component and the second component is 90% by weight or more, and the first component: the second component=20:80 to 100:0 is set, and a sealing material containing the sheet.