Dropped $180 on a "4 season" sleeping bag that left me shivering at 38 degrees in Shenandoah
Bought a bag rated for 15 degrees last October because the tag said "4 season" and I trusted the picture of the guy camping in snow. Took it out to Shenandoah in early November, temps only hit 38, and I woke up at 3am shaking so bad I had to put on every layer I brought plus my rain jacket inside the bag. The thing packs down to the size of a football, sure, but the fill is some no-name synthetic that clumps up in the corners after two washes. I paid $180 for it and a $40 fleece liner from Walmart kept me warmer on a later trip. Now here's my debate: do you trust temp ratings at all, or do you just subtract 15 degrees from whatever the company claims and buy based on that? Some folks say the ratings assume you're in a base layer with a pad rated for the same temp, others say the whole system is rigged to sell bags. I'm out almost two hundred bucks and a cold night, so I want to hear if you all have a rule of thumb or if I just got unlucky with a junk brand.
That 15 degree rule is real and most folks who camp a lot know it. Temp ratings on sleeping bags come from the EN 13537 test, and the number they slap on the tag is usually the "limit" rating, which assumes you're a warm sleeper in a base layer on a pad with an R value around 5. The "comfort" rating is what matters for most people and it's typically 10 to 15 degrees higher than the limit. So a bag rated 15 is really a comfy bag down to about 30 for an average guy, and if you sleep cold it's worse. Synthetic fill that clumps is a whole other problem, once it balls up in the corners you've lost loft and loft is what keeps you warm, no rating saves you there. My rule is buy 20 degrees below the lowest temp I expect to see, and pair it with a pad rated at least R-4, because the ground steals more heat than the air does. A $40 fleece liner adding warmth tells you the bag itself is the weak link, not your setup.
All true but people still ignore the comfort vs limit thing every single time they buy a bag. The 20 below rule is solid and the pad matters more than the bag half the time, cold ground will wreck you no matter what you're zipped into. Skip the liner and just get a bag that actually fits the temps you camp in.