Ed: Don't know what FR-1 is, but FR-2 is a flame retardant form of paper phenolic laminate. The numbers after the FR appear to be assigned by performance and cost. FR-2 is lower Tg, cost and performance than FR-4 which is lower cost, performance, and Tg than FR-5. Hope this was some help. Don Vischulis [log in to unmask] Ed Cosper wrote: > What is FR1 and how does it differ from FR4? ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################