Bag systems (bags with several layers you can add or pull off) have become more visible, but they do beg the question of actual performance versus acceptable compromise. After all, isn't a specific bag for a specific temperature and use far better and of greater value to you?

While manufacturers don't deny that bag systems are a compromise they assert that for many it is an intelligent compromise, and I agree. If you have a limited budget and are not at all sure if you might need a warmer or lighter bag as some point in the next year or two, you might want to consider buying into the system concept.

Sure, a specific bag that attacks a specific use is better than a system approach. After all, a system will generally weigh more and be more bulky. However, not everyone can afford the extra bags that might be needed. I have six different bags myself (4 down, 2 synthetic) and I could probably argue the case that I need a couple more.

For most people, however, that's not a viable approach, which is why some manufacturers, including Cascade Designs, Mountain Hardwear and Marmot offer the system approach. This type of program allows you to purchase the bag you want and then if, and I do mean if you decide at some point you want a bag that is a bit warmer, you can purchase an upgrade and zip it in or slide it in (depending on the manufacturer's specific design features), adding up to 20 degrees of additional warmth.