Leather bags are unique among men’s accessories.

A good one will last a lifetime and, if treated well, will look better at the end than the beginning of your life together.

Only leather has this attribute, gaining an individual patina from the way it is used and cared for, and a bag provides the largest canvas on which that beauty can be displayed.

The quality of leather attachés, holdalls and brief cases varies hugely. But unlike suits, the quality is on the outside, for everyone to see. You just have to know what you’re looking for.

The three main areas to watch are leather, hardware and stitching.

Good leather is the most tactile area. Pick up a soft example, like a holdall, and feel how supple it is in your hand. Try bending it inwards, towards the centre of the bag, and watch for sharp creases on the surface that show whether there is some kind of coating on the top.

A good leather will wrinkle naturally like skin – like the creases on your knuckles.

“The skin that comes from the cow is around three quarters of an inch thick,” says Bill Amberg. “That is split into two or three layers and only the top has a grain, and inherent strength.

“The mid-layer might be used on cheaper bags, but painted with something to give it a new surface. That will peel off pretty quickly.”

When it comes to hardware, zips are pretty easy to test. Try zipping them up and down; the smoothest are the best (if that smoothness lasts).

Checking the D-rings that join handles or shoulder straps to the bag is also quite straightforward: all hardware is either a cast fitting or pressed metal.

The latter is lighter, cheaper and weaker. You can spot pressed metal because there will be a faint seam somewhere on it, usually running around the edge.

“We use cast stainless steel or brass on all our bags,” says Max Summerskill at Dunhill. “Cheaper hardware is usually zamak – a zinc alloy – and it will often be the first thing to go on a bag. That’s incredibly frustrating, when a good bag is undermined by poor fittings.”

Dunhill still makes a small part of its leather in north London – part of the Duke range. The difference in price between Duke and other ranges, from around £1,000 to over £2,000, is due to the large amount of hand-stitching involved.

Stitching by hand is always stronger than a machine because it involves two threads interweaving through the leather. A machine can’t reach through and bring a needle back.

That’s the prime reason Hermès or Ortus bags are so expensive: they are 100 per cent hand-sewn.

In general, look for slightly longer, tighter stitches that seem to be pulling the leather together. It is most commonly used on handles on other bags (such as Louis Vuitton hard cases) and some traditional attaché cases.

“The most beautiful of all is the lid-over case, where you can’t use a wooden frame because of the way the lid has to fit over the base,” says Carol Bellingham at William & Son. (Louis Vuitton example below.)

“The structure there is created entirely through stitching into a solid piece of leather. Because it doesn’t have a frame it can’t shatter. Someone once dropped one from the top of the Eiffel Tower; that’s how we know.”

In the end, outside large designer brands, price normally reflects much of the quality of a bag.

But there are also many bags from reputable companies that look cheap – with shiny, artificial finishes or printed patterns – and plenty of good bags that skimp on the hardware.

If you want a bag that will last a lifetime, it’s worth checking for the aforementioned signs of quality. After all, all a man really needs in life is a work bag, a weekend holdall and a suitcase. Invest in all three departments, and you’re set.