They are printed on FOGRA approved paper. Which basically means that the paper is certified to be within a certain ISO colour standard. The have also been printed using one of the best CMYK simulation RIP's available (GMG). In a nutshell, the proofs give a very accurate simulation of what the final press output will be like.
It's been a very exiting and interesting project, working on this book, and I feel I've learned a lot in the process too.
Once I've approved the proofs, the next stage will be onto printing the book. I'll give you all more details about the expected arrival date of the book once we're past the proofing stage. Until then, I can't really say for sure just when the book will be here, but I'm hoping for sometime around October or November.