Fetching Windowpane Thornproof
Galloping over fields, hedges and bracken, or indeed when desiring to appear as if one has, a chap needs to look his best.
Not only that but it's never a bad thing in such circ.'s to be protected from scratchy thorns. Or indeed ladies' nails. Hence the thornproof, where the wool used to make the jacket is of such a tight and heavy construction that the jacket could conceivably be stood in a corner unaided.
That it bears a windowpane check is evidence of its being intended for the countryside where the rules on colour are more relaxed.
And if it wasn't fetching then a chap would hardly wear it would he?