hi I am new to this forum and new to climbing so I apologise for the novice questions.
I am currently buying gear to get set up to do some mountain climbing. I am about to buy both a belay parka and a hard shell jacket. Both are on sale at a good price. My question is with regards to sizing. Am I right to assume you will never be wearing both these jackets at the same time. eg the belay parka up high in cold weather and the hardshell in heavy rain where its a bit warmer. Therefore the hardshell will not need to be sized to fit over the belay parker and I could just go for a large with both?
Thanks in advance for any assistance.

A "parka" generally is already windproof and water-resistant, so there's not much point in adding a shell to it.

A "belay parka" means something you wear while belaying: standing around at one end of a rope while you partner climbs at the other end. For this purpose you want something extra-warm, properly fitting so you can get it on and off quickly, and light and packable so you can stuff it in your climbing pack without wasting time, weight, or space.

The same jacket can also be used in other situations where you need a lot of warmth, like hiking in deep winter and/or above treeline.

There are a few different ways to layer your clothing, there's no single formula that works for all activities in all conditions.

Depending on where and when you climb, it can make sense to have a windproof/waterproof layer that you leave on while climbing, and a warmer down jacket/vest that you throw on top of that whenever you stop. For this kind of system the windproof layer usually needs to be breathable, so a hardshell isn't the best.

For winter hiking I generally wear a fleece or two, with a light rain shell as a windproof top layer. If I stop or if conditions are extra cold, I'll wear my down jacket instead of the rain shell (or right on top).

For ice climbing I generally climb in a fleece, and use my down jacket as a belay jacket. If it's very windy (or raining - not that I recommend ice climbing in the rain) I'll keep the rain shell on while climbing and throw the down jacket over it when I stop.

That reminds me - for Christmas this year I think I'll finally get myself one of those newfangled "windshirts"

^^^ Love windshirts. Currently using a Arc'Teryx Squamish hoody, far and away my favorite piece of gear. I wear it almost daily in the mild CA Central
Valley 'winter', and it goes with me on every backcountry outing.

Belay parkas aren't always worn high and cold, and for that reason it's a good idea to get a synthetic one. A typical use case might be belaying a partner who is leading an alpine ice pitch. If you have been out in the elements moving up to the belayed pitch (e.g., wet snow or freezing rain) then you may need to throw the belay parka on over damp outer layers. Alternatively, a squall may start to make you cold and wet while you are belaying, and the fastest way to deal with it is pull out the belay parka. A Patagonia DAS parka or equivalent will keep you warm even if it gets damp on the outside and inside (from your existing outer layers), whereas a down parka which is not waterproof or has a waterproof outer layer may wet out from the inside and lose a lot of warmth. A classic use case for me was the North Ridge of Mt. Baker, where a single long, cold, windy and wet hanging belay session on the ice cliff justified the price of my DAS parka.

JHH60 wrote:Belay parkas aren't always worn high and cold, and for that reason it's a good idea to get a synthetic one. A typical use case might be belaying a partner who is leading an alpine ice pitch. If you have been out in the elements moving up to the belayed pitch (e.g., wet snow or freezing rain) then you may need to throw the belay parka on over damp outer layers. Alternatively, a squall may start to make you cold and wet while you are belaying, and the fastest way to deal with it is pull out the belay parka. A Patagonia DAS parka or equivalent will keep you warm even if it gets damp on the outside and inside (from your existing outer layers), whereas a down parka which is not waterproof or has a waterproof outer layer may wet out from the inside and lose a lot of warmth. A classic use case for me was the North Ridge of Mt. Baker, where a single long, cold, windy and wet hanging belay session on the ice cliff justified the price of my DAS parka.

This advise is spot on and very well describes why these parkas are so often referred to as 'belay parkas'. They are worn over the top of all layers, including a hard shell, so the hard shell should NOT be sized to fit over the belay parka. Climbers in the wet Pacific Northwest are connoisseurs of synthetic parkas. The Patagonia DAS is a lot of parka and might be overkill depending upon where you are climbing. Ice climbing in the Canadian Rockies or alpine climbing the AK Range are good candidates for the DAS (as well as being good candidates for down, since the cold climate means drier snow). Warmer ranges you might find a lighter weight parka (e.g. 100 gram Primaloft) to be more versatile.

I personally have three synthetic parkas, a Wild Things Belay parka (similar in warmth to the DAS), a Patagonia Micropuff, and a Patagonia Nanopuff. The WT Belay Parka goes with me to the AK Range and Rainier in the Winter, the Pata Micropuff goes ever where else in the Winter, Spring and Fall, and the Nanopuff is my summer weight parka in the lower 48. Of the three, the Micropuff has seen the most use, so much so I wore it out and recently replaced it with what seems to be the closest choice, a Mountain Hardwear Super Compressor.

This brings me to another thought about synthetic parkas. Primaloft is considered to be the gold standard of synthetic insulation. Light, compressible, and water resistant, the highest quality Primaloft is equivalent to about 450 fill power down. Primaloft has recently introduced a range of insulation products, the best of which is Primaloft Gold (formerly Primaloft One, the original offering).

The difference between Gold and the less expensive varieties is noticeable. I insist upon Gold. The new version of the Micropuff uses Primaloft Sport, which was noticeably more bulky and did not drape nearly as well as my previous jacket. I returned it and bought the Mountain Hardwear equivalent (Super Compressor), which uses a proprietary insulation which so far seems to be similar to Primaloft Gold in terms of compressibility, drape, and warmth.

The other factor to consider is weight. the DAS and WT Belay Parka uses 180 gram/m2 Primaloft. Three season parkas often use 100 gram, while summer weight often uses 60 gram.

Great advice from everyone thanks so much I will kelp all this in mind when purchasing a belay parka

Thanks again