PLASSEX is a forward-chaining rule-based expert system for plastic selection written in CParaOPS5. This system prompts the user for desired properties, and lists all plastics suitable for a particular application. At present, PLASSEX has 393 plastics in the data base and considers up to 39 polymer properties in order to select the right plastic. More properties can be added to the system with some understanding of the code. This system also provides the user with a help facility. PLASSEX has a number of other features; for instance it gives the user an opportunity to modify any property in case the system fails to come up with a suitable plastic the first time. © 1993 by John Wiley & Sons, Inc.