In the Card Menu, the balance visible under "Loopring balance estimate" represents an estimate of the fiat-denominated value of the cryptocurrencies deposited in the user's Loopring wallet (it can be in EUR or GBP depending on the country from where you ordered your eidooCARD).
In other words, "Loopring balance estimate" is an estimation of the available balance from which the eidooCARD can pull currency at the time of payment. Since eidooCARD allows you to spend your cryptocurrencies "on the fly" in a decentralized way, the balance can change because the underlying assets may be subject to price volatility.
