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
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Ed Cosper wrote:

> What is FR1  and how does it differ from FR4?

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