This question might seem silly, but...which kind of leather was in use in the middle ages for the strappings in plate armour?
All information I could collect so far is merely hearsay, an as I am not a leather specialist and can´t judge between leathers restored in the 19th century and probably period strappings.

What I heard so far is the following:

-they used fat-tanned deer or elk hide.
-thy used fat-tanned material because it does not affect the metal as oak-tanned leather does, because threre´s no tannine involved in the tanning process.
-they used any kind of leather, cattle, calf, deer, elk...

Of course, in any case I´d prefer vegetably tanned leather and keep away from chrome-tanned stuff. but basically, that´s all I really know;o)

Does anyone have any references in this question?

Thanks in advance ad best regards,

Ivo

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My limited observations suggest buff leather was used in preference. That is, cattle hide processed with oil, often fish oil, which renders it soft and supple like chamois leather.

But that's just more hearsay.