Which temperature rating should I buy

“I am currently buying gear for an up coming trip to the Northern Alps in Japan. I do not have experience with low rated sleeping bags. I cannot decide if I should purchase a 15F or 0F bag. I want to buy a bag that I can use for the next decade or so during early spring, late fall, and mostly winter time in the mountains. The last trip I went on was in April and the temp inside a four walled shelter was -3C. I was using a -5C bag at the time and I was warm at filling my stomach with fats and proteins, but cold prior to that. Any recommendations on which bag would better suit me in the long run?”

“Probably the 15, for Japan, go with a Montbell. :)”

“Sleeping bags are for sissy's.”

“Mostly winter? Zero degree. Get something with continuous baffled and down. This allows you to shift insulation from the top of the bag to the bottom and vice versa, effectivly allowing you to have a warmer or cooler bag based on outside temps. The other option is to get a 15 degree bag with a liner that will allow you to vary temp and weight based on whether you carry the liner or not.”

“I like Rosey's second option best. You can also take just the liner when summer camping.”

“It depends partly when and where in the Japanese Alps - at 10,000 feet, it can get pretty cold. You might look at forecasts or average temps for the dates you have in mind, adjusting for the roughly 3.5 F change per 1000 feet.”

“Western Mountaineering down bags are pricey, but very good quality. I love mine 0 degree bag by them, although where you're going you'll want something rated lower than that.”

“Is lean toward the zero... If its too warm you can just unzip it a little bit to get a draft. Better than getting a 15 and being too cold.

Besides, if not this trip, there may come a trip when you will need a 0 degree bag - it'll save you that expense later”

“..or you'll go on more trips at or above freezing but you have to lug that zero around.. I thought -3 c was the expected temp. 15 might be a little cool depending on the bag but I'd usually opt for smaller and lighter, especially climbing. Use the space you save on a good pad.”

“Awesome. I have thought about adding a liner as well. Thanks for all the suggestions. I am leaning towards the 0 degree bag. I really don't want to be caught with an inadequate bag. The trip is from Mt. Tateyama to Mt. Yarigatate the first week of October.”