Reference

Leather jacket hides and thickness, compared

The single most useful number on a leather jacket is its thickness, and almost nobody publishes it. Below roughly 0.9 mm you are buying a garment; above roughly 1.2 mm you are buying something that will outlast the decade.

Hide	Thickness	Character	How it ages	Best for
Steerhide	1.1–1.4 mm	The default for a jacket meant to outlive you. Stiff for a season, then moulds.	Creases sharply at the elbows and shoulders, darkens where it is handled.	Riders, truckers, anything that takes abuse.
Horsehide	1.0–1.3 mm	Denser and tighter-grained than steer. Famously stubborn at first.	The best patina of any hide — high contrast, almost lacquered where it wears.	Enthusiast choice. Buy it if you enjoy the break-in as part of the deal.
Goatskin	0.9–1.2 mm	Pebbled grain, unusually strong for its weight. What many wartime A-2 flight contracts used.	Softens without going limp; the grain stays visible for decades.	Flight jackets. Light on the shoulders without being flimsy.
Lambskin	0.6–0.9 mm	Very soft in the hand from day one, which is the whole appeal and the whole risk.	Scuffs and stretches. It does not develop a patina so much as wear out.	Fashion bombers and anything worn indoors. Most high-street "leather jackets" are this.
Water buffalo	1.3–1.7 mm	Heavy, deeply grained, oil-finished. A distinctly Asian hide with real substance.	Takes oil well, goes almost black at the wear points.	Field coats and anything that lives outdoors.

On goatskin, since it gets a bad name unfairly

Goatskin is sometimes dismissed as the cheap option because it turns up in inexpensive jackets. The hide itself is nothing of the sort — it is strong for its weight, holds a pebbled grain that stays handsome for decades, and it is what a great many wartime A-2 flight jackets were made from. The repro houses that charge four figures still choose it.

The hide to be wary of is lambskin: lovely in the shop, thin on the shoulder, and the usual answer to “why did my leather jacket wear out?”