## Chapter 27: Materials and Reactions

The tree view contains a `Materials` object and a `Reactions` object, which contain all the currently available materials and reactions.

A Material details view is available for editing the properties of new or existing fluids, solids, and mixtures. The new or modified materials can then be selected for use in your simulation or reaction definitions. For details, see Materials.

A Reaction details view is available for editing the properties of new or existing reactions. For details, see Reactions.

Note: You can set only those material properties that will be used in the CFD model. For example, you can set the buoyancy properties only if your model involves buoyant flow.

You can use CEL to define fluid property variation through an expression if it is required. For example, you could define `Dynamic Viscosity` to be a function of `Temperature`.

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