Hi @Matt1!

@Philreedshikes gave a great response here. 

I just want to add that while products like sleeping bags and sleeping pads do have a consistent, uniform rating system to describe their warmth, clothing does not. Anytime you see a warmth rating on clothing, it's generally manufacturer specific, and a general estimate based on in-house tests. 

That being said, there are some consistencies in clothing. For example, down fill power refers to the measure of down quality, or "fluffiness" related to the insulating power of the down. So 800 fill down will be warmer and lighter than 400 fill down if the same amount of down is used. However, there is no standard as to how much down should go in a garment, and any place where the garment has baffles (stitches or welds) to keep the down in place, there is no fill. This means that if a garment has a lot of baffles, it might be less-warm. (This is why some down jackets have many baffles in places where the body dumps lots of heat, like armpits). 

3M makes a synthetic material called Thinsulate which is used by many manufacturers for glove and boot insulation, and is rated in terms of the amount of grams of weave per square meter, typically anywhere from 100-400g. As the rating goes up, the warmth goes up. Yet there is no comparable equivalent rating among other types of synthetic insulation used in gloves and boots, and there is no standard for how the insulation is actually used in clothing. So, the warmth remains pretty subjective.

Frustrating, right? Ultimately, as Phil explained, the environment, a person's personal cold tolerance, and the activity all play a huge part in choosing the right clothing. The most important way to dial in warmth in consideration of those factors is layering. By layering, you can dial in an appropriate warmth for conditions.

Check out these Expert Advice articles on choosing insulated outerwear, and what to wear backpacking for more on clothing and layering.

Hope this helps!

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