Creo Simulate > References > Fundamentals > Working with the Model > Layers > Layer Basics > About Layer Names
  
About Layer Names
Layers are identified by their names. Layer names can include alphanumeric characters, underscores, and hyphens. You cannot begin a layer name with a hyphen “-”. Layer names can have a maximum of 31 characters.
Layers displayed on the Layer Tree are first sorted by their numeric names followed by the alphanumeric layer names. Layer names that include the alphanumeric characters are sorted alphabetically.