FLAC for lossless audio?

We are working for a Dubbing company who uses (sorry, used) FLAC as an exchange format.

The need to send us large audio + video projects, to which we need to add our stuff.
Because of the size of the projects, they try to minimalize the up/download times.
Which makes sense.
However, our delivery format is .wav.

Have to say that they have stopped doing this, because a few of their foreign studios are on PT.
And internet connections have become so fast that it is hardly an issue anymore.

Fredo