The word flippable sounds like a valid word, but should not be regarded as formal English. It is not considered a flat out error though.
There are some formal words like adaptable that have become more standard and have an -able ending, and have become more formal, mostly through Latin and French.
Better alternative for flippable Other alternatives for flippable could be turnable or interchangeable. Interchangeable could be a better alternative than turnable, the Oxford English Dictionary considers interchangeable a word, but not turnable. Interchangeable being used for mutual substitution for something else, (the next card).
I wouldn’t say that turnable or interchangeable would be a better alternative for flippable since flippable has an obvious meaning as @nnnnnn noted.
Flippable would be acceptable most times, and understood most times, but wouldn’t always be regarded as “formal”. As for a more formal replacement, interchangeable would be a more formal alternative, but isn’t always a perfect substitution, it depends on the context.
As for adding -able to verbs you can check out: