Clairefontaine make excellent paper for fountain pen users, and they make it for their sub-brand Rhodia too. It's so good that you may well want some that you can put in your pocket, and here it is.
Now, it has to be admitted that there is some room for confusion here. These are marketed as A6, and I believed that when I first carried one for a year. It survived the use and abuse without any difficulty - which is one of the reasons I recommend it - but then I realised that it isn't actually A6. It's Pocket Size, which is 9cm x 14cm; A6 would be 10.5cm x 14.8cm. These things matter to some people. If, however, you're not one of them, this is pretty much irresistible.
Here, then, are three rock solid reasons to take the plunge. Firstly, the paper is thin enough not to be too bulky, but it can handle real, juicy nibs too. Secondly, the firm PVC covers are hardy and really take the abuse (and you can, if you wish add a pen quiver as I did). Thirdly, it comes in very groovy purple (other colours are also available) and has rainbow zebra end papers, which are surely indispensable.
Finally, as if any further persuasion were necessary, Nero's Notes has them on special offer at the moment. All this for a fiver? Snap 'em up!