Founded in 1875, Liberty London is one of the UK's most iconic department stores, stocking fashion and accessories, homeware, beauty and haberdashery products. Liberty keeps in contact with customers via a loyalty scheme, Liberty Rewards. Members receive invitations to shopping events, sales previews and special offers, as well as twice-yearly reward vouchers. Liberty segments its customer database according to spending habits: recency, frequency and amount of spend - and this information is used to decide who receives which mailings and when.

Liberty uses direct mail, email and SMS to communicate with customers - but it is mail which produces the best results. Not only are response rates to mail more pronounced, but Liberty believes it is a medium which is particularly suited to the promotion of a luxury brand. Liberty wanted to fine-tune its direct mail to make it even more effective.

Liberty consulted Royal Mail, which presented them with the results of eye-tracking research. Eye-tracking is a form of research that monitors eye movement - where people look when they receive a piece of mail, or look at a website, and why. The research revealed which design elements encourage people to open an envelope, read the contents and respond. Previously, Liberty's direct mail was delivered in a plain envelope, with a Liberty logo on the outside. But the eye-tracking research showed that this wasn't enough.

'Look inside for your Liberty Rewards' was added to the outside of the envelope. This very simple change increased redemption rates of the vouchers inside the envelopes by 5% to 60% overall. For high-spending customers, the increase was even greater.

That the design and layout of direct mail is crucial - a tiny change can make a big difference to how effective it is.