Less-expensive bags generally tend to be made from synthetic materials, which isn’t a bad thing. If you’re just looking for a bag for camping, one you don’t have to port with you, synthetic bags can be warm but are also a little bulkier because they need more material (loft) to keep you warm. Down bags tend to pack down a little easier than synthetic bags, but if moisture gets on them, they tend to take longer to try (and you might be a little cold in the meantime).