I have read that at the slightest hint of rain, English warbowmen would unbrace their bows and call it a day
That's news to me, despite the account of men keeping their strings under their hats at Crecy.
There are accounts enough of fights in inclement weather.
What about Towton, for example?
If the string was an unwaxed spare, I might put it under my hat rather than subject it to a soaking, not for fear of it breaking, but not wishing the relaxed string to take on too much moisture.
Having said that it is likely that a well waxed string, twisted and taut under bracing tension, would be far less prone to absorbing moisture.
With a linen string what I do not want are short fibres and dryness.
Our linen industry in it's heyday was based in Lancashire and N.Ireland just because a damper climate was necessary for the machine production of linen thread, it being more too prone to breakage when spun in dry conditions.
Rod.