There are three simple things you can do to put a sleeping bag with a minimum of effort and crush it down to the smallest possible size. First, Compress it by the tail. Second, turn it upside down. Third, use a compression bag. Here are the details on these simple but extremely effective techniques.
Compress it by the tail
The most common mistake that people make when filling a sleeping bag is to hang it on the hood, first, leaving the tail (where your feet go) stirring there until the end. The problem is that the foot box of a sleeping bag is a closed space, which means that it usually turns into a balloon filled with air if it is the last thing that goes into the bag. Hassles and disadvantages arise when you spend time slowly forcing the air through the fabric and insulation. If, on the other hand, you start with the tail (as shown here), all this air escapes easily, leaving you with the hood open and easy to fill at the end.
Turn it inside
This second technique is generally applicable only to certain types of sleeping bags, namely styles that include an additional layer of wind and water resistant fabric on the surface (a common feature on winter sleeping bags) . This feature can be great to block the air flow from the outside, but it does a great job of keeping the air inside as well. Filling a bag like this can be an enraged exercise in balloon deflation, even if you start with the tail. The solution is to put the bag upside down, which positions the wind-resistant fabric as the innermost layer of the bag, making the filling instant.
Use a compression bag
In general, it is nice to crush your sleeping bag on its smallest possible size. This may require considerable effort if you stick the bag in a standard material bag, just barely big enough. On the other hand, the compression bags have a series of straps which connect the two ends of the bag of material, generally via a separate cover that you place on the closed end (as illustrated here). Once the bag has been padded, you simply position the lid and miss the straps to crush the bag to a minimum size.
The other major bonus of the compression bags is that you can buy one with enough room to easily fill the sleeping bag before compressing it, which can save you a lot of effort. Just make sure it’s not so wide that you can not compress it to the maximum, if you can completely reduce the straps, that’s too big.