Surprising as it may seem, most budget travelers don't need to carry a sleeping bag. Even in winter, it's very rare to find accommodation cold enough to need one. You can almost always rent or borrow extra blankets if you need to, even in budget accommodations.
Most hostels in Europe, Australia, and New Zealand ban sleeping bags completely due to concerns over bed bugs, and even the smallest ones add extra bulk and weight to your luggage.
Unless you know you'll be hiking or camping on your trip, there's very little reason to travel with one at all.
A sleeping bag liner, however, is a different story. It packs up into a tiny ball, and is so light you won't even notice it's in your bag. It's more than enough bedding for warm climates, and adds extra insulation if you do happen to get cold at night.
It also serves as protection against bed bugs, mosquitoes, and other insects while you sleep, which in many parts of the world can justify its inclusion by itself.
Here's what to look for when purchasing a sleeping bag liner for your next trip.
Silk Is Best
While cotton liners are cheap and easy to wash, they're rarely the best option. You'll quickly start sweating inside them in warm rooms, which soon makes them damp and smelly. It's not always easy to dry them out properly either, especially when you're on the move.
Silk liners are a much better choice.
They're more expensive (in some cases, significantly so), but this is a case of definitely getting what you pay for. Lighter and less bulky than cotton equivalents, they wick moisture away from the body, and dry quickly if they do get damp for any reason.
For this reason, they tend to need washing less frequently, which is a definite bonus for travelers.
When the time does come, though, you can wash them on a gentle cycle in a normal washing machine. Just remember to avoid using fabric softener, and hang them up rather than putting them in a dryer.
Silk liners are also breathable, which is a godsend in hot, humid climates, and bugs aren't overly keen on them either. This doesn't mean you can't get bitten while using one, but bedbugs in particular are unlikely to nest in them.
Insecticide Is Better Than Bug Bites
While sleeping in an insecticide-infused sleeping bag liner probably isn't anybody's first choice, neither is waking up with hundreds of bug bites. This is especially true in countries where mosquito-borne diseases like malaria, zika, and dengue fever are a concern.
Unless you know you're allergic or sensitive to it, look for liners treated with Permethrin or similar to help keep the bugs away, or consider applying it yourself after purchase via a pump or aerosol spray.
The treatment will last for several weeks or washes, and it's quick and easy to reapply at home once it starts to wear off. Just remember to spray while outdoors if at all possible, and keep pets well away. There's no need to completely saturate the liner with your spray, but do try to fully cover both front and back sections.
Even after spending more than two months using a silk liner while staying in dorm-style accommodations on the Camino de Santiago hike through Spain, this writer never suffered from insect bites during the night. Given the prevalence of bedbugs in the hostels, especially in summer, that was no mean feat.
Rectangles Are Where It's At
Liners, like sleeping bags, tend to come in one of two shapes, rectangular or "mummy", where the bottom is narrower than the top. Unless you're planning to regularly use your liner inside a mummy-style sleeping bag, opt for the rectangular version.
It gives your legs and feet more room to move around, helping prevent them from getting hot, and you from feeling any more constrained than necessary. A little extra room to move goes a long way.
There are many different manufacturers and models of silk sleeping bag liner out there, but either of these options would be a solid, reliable choice.
The Sea to Summit Premium Silk Travel Liner comes in a travel-specific version that includes an inbuilt pillow liner, as well as standard rectangle and mummy options. It weighs six ounces, and has stretch panels along the seams. Those panels make the liner easier to get in and out of, and let it move with you during the night.
The Cocoon Silk Travel Sheet is a lightweight rectangular or mummy liner that comes in a range of colors. There's a cotton version as well, but as mentioned earlier, little reason to choose it. A side opening with Velcro fastenings makes climbing in and out a breeze, and like the Sea to Summit model above, there's an enclosure for your pillow as well.