Which sleeping bag liner should I choose?

This is a hugely personal choice, and can't be answered in a single quick answer.

A really basic primer looks like this: the Silk, Silk/Cotton, and Expander liners are aimed primarily at travelers - they offer a clean, hygienic sleep environment wherever you find yourself at the end of the day.

The Silk and Silk/Cotton liners can be used for backpacking and will add some warmth, but not as much as the knitted Reactor and Adaptor liners. Expander liners are generally considered to be too heavy and too bulky for backpacking; they are used for static camping.

The Coolmax Adaptor liners are designed for use inside sleeping bags in warm and humid weather. The Coolmax fabric does not cool you down, but it spreads perspiration effectively so it can dissipate effectively. This process (known as moisture management) prevents you from feeling clammy on warmer nights. When the weather is really warm, you may just sleep in an Adaptor instead of a sleeping bag. Adaptors are great for anyone who prefers a stretch knit fabric (like a quality T-Shirt) instead of a woven fabric - Adaptors are therefore popular with travelers as well as backpackers. Consumers based in the USA can also purchase Insect Shield-treated versions of the Adaptors which offer great protection against certain insects.

The Thermolite Reactor liners are made for increasing the warmth of your sleeping bag in colder temperatures. Hollow-core fibers trap insulating air, a factor enhanced by the 'three dimensional' knitted structure of the liners.

Reactors can be used as standalone sleeping bag substitutes in warm weather (just be aware that they are not windproof - moving air will take away the warmth you have generated.

If you have ever tried a liner and found it to be constrictive, we would direct you to the Adaptor, Reactor, or Expander series – all three are made of really stretchy fabric.