(CNN) -- Why does French dressmaker Chanel always seem chic? What does British seamstress Vivienne Westwood have that others don't? And even though it's been 25 years since "Top Gun", why does everybody still want a pair of Ray Bans?
The short answer is, they're just really cool.
It might be a subjective concept -- one man's cool Hawaiian party shirt is another's discarded Christmas gift -- but certain brands do seem to stay in fashion forever.
It's a phenomenon highlighted by the UK's annual top 20 "Cool Brands" list released today.
Top of the pile is Aston Martin, James Bond's car-maker of choice, followed by Apple and motorbike designer Harley Davidson.
But numerous fashion labels make it onto the list, with Rolex highest among them at number four, followed by Nike, British designer Alexander McQueen and perennially cool Ray Ban sunglasses.
So, how did these brands manage to acquire this ineffable quality -- at least in the eyes of the Brits? We ask chief executive of the Centre for Brand Analysis and "CoolBrand" council chairman Stephen Cheliotis for his six rules of cool.
1. Style is everything
From the door handles to the website and the tags on the clothes to marketing events: If people are to be persuaded a brand is the height of cool, the devil is in the detail, says Cheliotis.
"It's not just about making your clothes look good," he insists. "Absolutely everything associated with the brand has to exude style -- from the packaging to the company website, to the type-face on the inside label."
2. Never try too hard
No one likes a busybody and, says Cheliotis, even the word "cool" suggests a certain relaxed approach. "The original idea of being cool is being laid back, not running around like a headless chicken trying desperately hard to please everyone." This, he says, is true for people and fashion brands alike. So, if it feels like a brand is trying way too hard to impress -- chasing every trend going, for example -- then it probably won't.
3. Stay true to the brand
It's not cool to fake it. In other words, if a company began life selling pretty knitwear, it should think very carefully before venturing into, say, leather jackets. "You must always remain true to your roots," instructs Cheliotis. "Shoppers want something authentic and it's obvious when you're out of your comfort zone."
Designer Alexander McQueen may have recently passed away, he adds, but it doesn't mean that his eponymous label should be tempted to change its style. "As long as it (the label) sticks to his original vision it will probably stay on the list."
4) Keep evolving
This might sound at odds with the previous rule but, according to Cheliotis, it's certainly not. "One of the reasons we keep seeing the same brands on the list, like Nike and Rolex, is because they're always innovative, but at the same time they retain their core identity."
5) Don't be promiscuous
Some fashion houses squander their hard fought cool rep by plastering a company logo on everything that moves. In Cheliotis' view, bootmaker Dr. Martens have been guilty in recent years of such profligacy.
"They were known for making really sturdy, simple and good quality footwear. Now they've plastered their name on everything, it's cheapened the brand and undermined their core product."
6) Be humble
A stark word of warning for self-satisfied designers everywhere. "Successful brands don't fixate over being cool, instead they just do their own their own thing, stick to their founding principles and follow what they think is right," says Cheliotis. In other words, if you think you're cool, you probably won't be for much longer.