WRU academy players will join Cardiff Blues stars Roberts, Sowden-Taylor and Osprey Thomas - all the action takes place outside the Capitol shopping centre on Queen Street.
Rugby fans, shoppers and casual observers are all welcome to pick up training hints and tips, and take part in a range of activities including the Under Armour Performance Challenge, using scrum-half passing and lineout throwing equipment provided - with activities for all ages and first team shirts among a variety of prizes.
For a chance to meet some of Welsh rugby's brightest stars on the eve of preparations for the Invesco Perpetual Series in which Wales play host to South Africa, Canada, New Zealand and Australia at the Millennium Stadium in November, simply turn up at any time throughout the day.
Also on hand will be Under Armour performance training guru, American, Todd Durkin and all the stars will be meeting and greeting fans, answering individual questions and handing out free gifts as well as showing off the full range of new Welsh rugby kit hitting high street shops.
"Welsh rugby has one of the greatest fan bases in world sport and our fans will use the clothing to show their support for the national side," said WRU Group Head of Marketing Gwyn Dolphin.
"They want clothing they can wear with pride and which has all the benefits of the performance-enhancing qualities of the Under Armour brand.
"For that reason we wanted to launch the full range of gear, along with the change strip, in a deliberately public way.
"We are putting on this free day of entertainment and interaction with some of our international stars with the explicit aim of giving something unique to Welsh rugby fans and consumers."