Add an extra, abstract spatial dimension to a model from the Definitions toolbar or right-click the Global Definitions node (), and then from the Extra Dimensions context menu, choose 3D, 2D Axisymmetric, 2D, 1D Axisymmetric, or 1D to add an extra dimension to the selected space dimension (requires that Advanced Physics Options is active on the Show menu). An Extra Dimension node, in the chosen space dimension, is then added under the Global Definitions node in the Model Builder. You can add one or several Extra Dimension nodes. It is also possible to attach an extra dimension to several components. Extra dimensions can be useful, for example, to model transport and reactions in two different scales, where one scale is the homogenized scale of a set of larger pores between particles or larger cracks in rocks, and a second smaller scale is the one inside porous particles or in porous rock.

The added node then contains these default nodes: Definitions, Geometry, and Mesh. The settings for the Extra Dimension are the same as for the Component node, except it has a unique Name.

The default node label in the Label field is Extra Dimension 1 for the first Extra Dimension node. The component name is a string used to identify variables in the model. The default Extra Dimensions component name is xdim1, xdim2, and so on, but you can change it in the Name field.