A Bling card is a gadget that you can add to any card in your Pack (except a PackPet), to further decorate it. Bling cards can be won in FlipRat, found in draw cards, or purchased from the premium markets (Las Vegas and Alcatraz). Bling cards cannot be traded, stolen, or locked in your Pack.
Once the Bling gadget has been added, you may remove it if you wish by using a 'scrubber' gadget, which will wipe the bling off the card and return it to its original form.
Bling can be added on top of a card that is already foiled, but doing so will remove the foil background. If you decide to use a scrubber to then remove this bling will not restore the foil background.
For more on Bling cards, please check out the following article.