The following link is recommended for those planning to visit the Berwyns. There isn't very much on the internet for hikers.
Ordnance Survey Explorer Map 255
What equipment should you take on a hike in the Berwyns?
Depending on the time of year, you should prepare for the worst conditions possible, even if there is not a cloud in sight at 6 a.m. and the weather forecast is good. Weather patterns can change quickly. The Berwyns are drier but colder than most Welsh mountain ranges and there is very little shelter once on the top.
The obvious items for cold weather include hat, neck gaiter or scarf, several layers including wicking t-shirt, good quality waterproof jacket/anorak, gloves (preferably waterproof), trousers (polartec or similar in cold weather) with waterproofs over (strongly recommend Marmot brand as they breathe), liner socks under thick hiking socks, and finally good quality hiking boots with ankle support. Additional equipment should include map and compass, whistle, additional water and rations for an emergency, as well as a lightweight foil emergency blanket.
Useful equipment should include shades (as much for the wind as the sun), GPS, multi-purpose knife, staff or stick, first aid kit, lip balm, small flashlight and spare batteries
Optional items would include a camera, binoculars and swimsuit (summer only!).
Isn't GPS "cheating"?
Not really, but always think of GPS as a back up, not an essential tool. Batteries fail. Besides you still need a map and compass, even with a GPS unit. Look at it this way, with dense fog and no land marks visible, wouldn't a previously entered waypoint or two be useful in getting you off the mountain?
Any recommendations on food for the trip?
The cafe at the waterfall was opening up as we began our hike so don't rely on them for sandwiches! We took hot soup in a thermos and enjoyed it on the summit. All the usual trail foods will work on the Berwyns, just make sure you have a little extra!
What about camping?
Obviously, as we made this a day trip we have no first hand experience. In the summer the cafe at the waterfall operates a small camp site.
Bivouac camping on the mountain is certainly a possibility but remember that is is private land and the owners almost certainly will not give you permission. We noted several good spots to wild camp (using the wildcamping etiquette of pitching late in the day, striking camp early in the morning).
What do you recommend for a first timer to the Berwyns? What will you do next time?
The trails we took are the best introduction to the Berwyns. Long hikes from one side to the other are possible but then transportation becomes a bit of a problem.
We will probably hike in from the east next time and take in both Cadair Berwyn and the northern peak, Cadair Bronwen.
What about public transport?
The nearest train stations are probably Gobowen, near Oswestry, and Welshpool. Both have connections to Shrewsbury and Birmingham.
Local bus services may exist as far as the towns down the valleys but they do not extend up to places like Pystyll Rhaeadr. The Berwyns are a lot more remote than many of the more popular Welsh destinations.