The pack contains a letter made from chocolate that companies can use to write personalised messages to customers, and has been developed by Proximity London after research from Royal Mail's partner Brand Sense, a sensory branding consultancy.
A study by Brand Sense found consumers made decisions to buy particular products based on their ability to engage "sensory signals". Royal Mail said the chocolate mailing would allow direct marketers to engage with more than three of their recipient's senses and improve campaign response rates for businesses.
The chocolate mailing, which contains a heat sensitive cover, has been sent to 1,000 people at marketing and creative agencies in the UK to show how it could improve response rates on direct campaigns.
Amanda Phillips, chief executive at Proximity London, said: "Royal Mail wanted to highlight the role that direct mail has to play in building brands. We came up with the concept of a chocolate letter because it is simple but powerful and illustrates direct mail's exceptional capability to engage all the senses."
Antony Miller, head of media development at Royal Mail, said: "Direct mail has for a long time been typecast as a predominantly response driven marketing medium by many.
"With this campaign, we really wanted to shatter this misconception and demonstrate the flexibility of the medium by showing how it can enhance brand engagement and build deep and meaningful relationships with consumers."