Originally Posted by jzmtl
Pure insulation value wise, nothing come close to good quality (800 fill power) down, even best synthetic insulation like primaloft one is only comparable to 550 power down, fleece isn't even on the same chart.
True to a point. The real difference outdoors is less dramatic. An inch of down insulation isn't any more effective retaining heat than an inch of Primaloft One, everything else being equal the down garment will just be lighter. In actual use the Primaloft garment will be more consistent for warmth and less effected by environmental/use such as moisture, compression of the insulation or insulation shifting leaving a cold spot. Down will just weight less. It is the weight of the Down that makes it such a good insulation compared to other materials. Down does have its place in the out doors, no question. To be the most effective insulation 800 fill down is the obvious choice. Most often it is not 800 fill down. The reality of down is limited by a few factors that Primaloft or even a decent pile garment are not effected by. Down will fail for several reasons, moisture..either from the outside (rain) or the inside (sweat), and compression. Down garments being compressed under a shell is a classic example of how a down garment can be limited insulation.
No clue where the OP is. I'm in the PNW. The climate you are in will effect what is a better choice as well. Dry like Colorado or Alberta or wet like the PNW. Dry is always going to be a better place for down. I have several down jackets. One in particular, a Eddie Bauer Microtherm BC, is really amazing for it's light weight compared to the level of warmth offered. But I wouldn't layer over it. One of down's greatest attributes is how well it breaths/passes moisture. Stick down in as a mid layer buried under too many shells and you are likely to get the down (the actual insulation) wet/damp from body moisture alone. The resulting warmth of the garment will quickly go down hill.
If you are using a garment a lot, cleaning becomes an issue. Some down garments you can throw in the washing machine and then machine dry. Even the ones that can take that kind of abuse it isn't the easiest task to get it cleaned and re fluffed. Synthetics are simple much easier to care for and more durable in my experience.
If one were to ask what is the warmest and lightest jacket, my answer would be down. The warmest and most durable/reliable jacket, Primaloft One. But there are so many other factors you need to consider. Including how active or inactive you will be and the environment you'll be in.
When you start layering it is a totally different game. Best warmth for the weight layering.....no question it is a good 800+ fill down vest. It allows a good bit of body moisture to escape instead of being caught up in the insulation lowering the down's effectiveness. In the right conditions a down sweater might be the best choice for additional warmth. I just don't see it here.
Same reason so many like the Atom Lt. The breathable mesh side panels help keep the insulation (and you) dry while offering a good layer of insulation. But a better used pattern for a synthetic than a down garment if you want to layer with it, as a similar down garment will wet out quicker in the same application with the resulting loss of insulation/warm.
Bottom line? How do you choose down over a synthetic? If you can keep it dry nothing better than a good down (750+ down) for a warmth to weight ratio. If you know you aren't going to be able to keep it dry, from the inside or outside, a synthetic is likely a better choice.