What is down? Down is the fluffy clusters found under geese, ducks, or any water bird. The down is the soft cluster that is gathered from these birds in slow processes to ensure wildlife preservations. Sometimes the down is harvested from nests after the birds have shed their winter clusters. The down comforter and down pillows are main products supplied by a bed linen store as essentials for completing your bed linens. For instance, a down comforter has these down clusters stuffed in a breathable cotton covering (duvet) that will create warmth. You will want to know how much warmth when purchasing it for your new bed linens. How to control the amount of warmth comes from the amount of down in the comforter along with the size of the down clusters. That is where fill power comes in - Fill power is the measure of loft in 1 ounce of down. The larger the cluster of down, the more fill power and the more warmth. That is why the higher number for fill power in a down comforter costs so much more. It depends on the region origin of the down cluster and how difficult it is to gather the clusters. The best guide for purchasing the down products you like is by deciding how much you need extra warmth in the coldest months of the year. Mostly, we go between light weight and medium weight for decisions. The heavy weight can be too hot and uncomfortable for USA climates. If you just want to buy a down comforter for a duvet cover look without including it's main purpose for warmth, best choice is a light weight duck down product and that is minimal purchase priced. Light weight down comforter in a White Goose Down product with a down proof ticking cover of 300 thread count of less is a basic. You will want the down proof cover for many reasons, one being to keep the down inside the down comforter besides being able to wash it without it falling apart. (use an approved down wash product).