Spencer Allenwrote a review of Western Mountaineering Sonora Sleeping Bag Liner on October 3, 2019
Familiarity: I've put it through the wringer
I took this liner on the PCT this year and its the best liner out there. The main reason I took this liner was to protect my Western Mountaineering Versalite because after hiking 15-30 miles a day you get real sweaty and gross and if you hop in your sleeping bag without either showering or having a liner it'll decrease the life of the bag tremendously. I bought a $700 bag for a reason because it'll last a lifetime. And with this liner, it'll last that lifetime looking ( and smelling ) a lot cleaner, and warmer as when down gets dirty ( from sweat and grim on you when you get in it ) it'll lose its loft and in the world of insulation loft is warmth. So I choose to spend a little extra money and weight to have my bag work as it's supposed to. Another plus to having a liner on a thru-hike is you now have a laundry bag when you need to wash your clothes in town. As well as washing the liner which will, in turn, keep the sleeping bag cleaner. Its a no brainer to me to have a sleeping bag liner. It also adds a couple of degrees of warmth which is always a bonus on those chilly nights. I'll continue using this any time I use a sleeping bag.
Picture: If you use a liner and keep it dry your bag will be just as lofty even after 100+ nights in it.