# Why do custom materials in Electromagnetics not include custom B-H data? - I have to start from scratch every time

**URL:** <https://www.simscale.com/forum/t/why-do-custom-materials-in-electromagnetics-not-include-custom-b-h-data-i-have-to-start-from-scratch-every-time/101403>\
**Category:** Vote for features!\
**Created:** [October 27, 2026, 5:42pm UTC](https://www.simscale.com/forum/t/why-do-custom-materials-in-electromagnetics-not-include-custom-b-h-data-i-have-to-start-from-scratch-every-time/101403 "2026-10-27T17:42:01Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![david\_gmail](https://www.simscale.com/forum/letter_avatar/david_gmail/32/6_22734026db12803ebb3e059622ac3534.png) [@david\_gmail](https://www.simscale.com/forum/u/david_gmail)\
**Post date:** [October 27, 2026, 5:42pm UTC](https://www.simscale.com/forum/t/why-do-custom-materials-in-electromagnetics-not-include-custom-b-h-data-i-have-to-start-from-scratch-every-time/101403/1 "2026-10-27T17:42:01Z")

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I can copy similar materials to my custom library, and make some changes. But it only allows constant permeability. So every time I want to use a specific custom material, I have to modify it, with all lthe potential for getting it wrong (has already happened once)