I used rubber chippings for three years in the base of my run before I got the roof covered rhis summer. There were considerable advantages over using woodchips, in that the rubber was always soft, warm and dry to touch, being totally non absorbent and springy to walk on, with no fungal spores such as you get with organic coverings when they become wet. When installed correctly over a liner of permeable weed proof membrane the earth below didn't get dug up into them, which would have made them dirty, (though this would have been the case with any sort of floor covering.) I never got puddles in the run because even in wet weather the 4 ins. Layer of rubber chips suspended the hens feet above the earth until it had drained - though my run is well drained and not prone to flooding anyway.
The main problem with them is keeping them clean, I found. Yes you can hose them down, (though this uses a lot of water if you are in a meter, and makes the floor of the run very wet, especially in winter when the ground is saturated anyway) When they are new, for perhaps the first few weeks or months, this seems to work OK, but after a while, if you dig down to the base of the chippings, you will find that there will be a layer of insoluble 'strainings' from the droppings which accumulate over time. Most of the poo is soluble but there are fragments of bits of grass etc which dont pass through the permeable membrane and in time this forms a thick layer which reduces the drainage and turns to sludge in wet weather. After hosing down i used to disinfect the run but this really only seemed to reach the top layer of chippings, not the rather smelly layer at the bottom. The next stage is that this layer gets dug up by the hens and begins to coat the chippings so they are no longer nice and black but look muddy and not so clean even when washed. I got to this stage, despite careful poo picking where possible, after about two years. During the last year I poo picked clumps of chippings into a bucket and washed them through a garden sieve. This resulted in lovely liquid manure for the garden, but was quite a task especially in wet weather in winter when the hens spent more time in the run so it got dirty faster. Poo pucking is quite tricky with rubber chips as the poo sticks to the chips but you cant put them on the compost heap, so washing them is really the only way to keep them clean. Then, this summer, I had an operation which meant I couldn't lift buckets of water and I gave in, got the run properly roofed and the chippings removed, and substituted Aubiose. This is wonderful in a covered run - so light, both in weight and in colour, makes the run much lighter than the black chippings. It's very absorbent so poo picking is really easy, the hens love digging in it, and it's blissfully warm and soft. I was just sitting there this morning in the sunshine, watching my girls scratching around, and was very glad I'd got things sorted out before winter set in.
I'd certainly recommend the permeable membrane over the floor, whatever you cover it with, and if the run has no roof I'm not sure what would be best to use. The idea about rubber chippings is that they last for ever, which is true, and they would remain as good as new if you could wash them really thoroughly, but it's not a task for the faint hearted. I did wonder about tumbling them in disinfectant solution in the cement mixer, but they are heavy and bulky and it really didn't seem as if it would be worthwhile for me anyway.