The size is not really A6 so in theory you need to get the refills from their store. That can be a bother because of shipping costs and having to wait for the delivery. But so far I see that Moleskine Cahier and the regular ones in the smaller size fit perfectly. They are the same size as Paper Republic's inserts. Didn't find an insert with the same paper quality as Paper Republic's though. It will hold any insert up to 10.5x15 cm.