Slash-sheets are dielectric material specifications sheets detailed in an appendix to IPC-4101.  The pages provide material specifications, such as coefficient of thermal expansion, glass transition temperature, resin content, glass type, etc...

Material vendors such as DuPont, Isola, Rogers, etc... create cores that satisfy particular requirements, for example /28 or /41.  PCB engineers that specifically require Isola-370HR might pay more than an engineer that simply request a material that satisfies /98 or /99, since a manufacturer might have a similar product on hand from a different manufacturer.

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