What is a Slack Value in separately mesh panel in Icepak?
When the Mesh separately option for an assembly is turned on, the offset added to Assembly in respective direction is called Slack Values.
By default the slack values are zero in all directions. However, in order to use non-conformal mesh the slack values should always be a positive number except it can be zero when the non-conformal boundary touches a hollow object or cabinet boundary.
The Slack values should be specified in such a way that cells on both the sides of interface are either fluid or solid, with the same material, and it does not violate any of the "Non-Conformal Assembly Rules" given in attachment.
For additional information, refer following section:
Icepak 12.1 User Guide -> Building a Model -> Custom Assemblies -> Editing Properties of an Assembly