Whether you want some extra protection and some peace of mind in your hotel room or are just camping out in a 3 man tent in a back country campground in freezing winter, a sleeping bag liner will definitely make the experience a lot better for you.
These liners are traditionally meant to provide addition layers of warmth while you sleep inside of a sleeping bag. Trying to add a layer of warmth between your body and the outside environment has the ability to significantly elevate your body temperate which could help when you are outside during the dead of winter. The same idea also applies to a double paned house window–keeping you insulated is important. Even through the use of a simple silk sleeping bag liner, your body will gain added warmth.
When you go out and purchase a sleeping bag liner, there will be many options to choose from. Depending on your requirements, many different types can work well for you. If you are searching for the simple liner that serves as a proper barrier between your hotel sheets and your body, the simple cotton or silk liner will do the trick. If you are trying to go out in cold camping weather, the fleece sleeping bag liner might be a better option. Whenever possible, you should stick to the brand that will likely give you the best possible fit. This is especially the case if you bought a mummy bag. You will definitely need to buy a mummy sleeping bag liner in this situation. For all others, you could find universally acceptable liners, but those could also be cumbersome to put into your bag. There are many companies like North Face, Marmot, and Kelty who have a line of sleeping bag liners for their own bags. Kelty has lightweight fleece liners that could also double as blankets.
You can also easily make a liner. Lightweight materials or fleece along with some Velcro is all you will need.You do not need to create a pattern for your liner, so the process should not be too hard. It will definitely be useful if you buy or make one for yourself.