Original review: The item description clearly says this is for 32oz wide mouthed Nalgene bottles and one is even pictured inside of the insulated pouch. However, none of the Nalgene bottles I have actually fit! They will go about 1/3 of the way without too much effort, but I was unable to get further than 2/3 even when pulling downward on the insulator and banging the bottle against a hard surface. If anyone has any secrets please let us know!
Update: I eventually was able to get the bottle into the insulator after sliding a butter knife between the bottle and insulator and tugging, twisting, pulling, and banging. Once you insert the bottle a couple times the insulator will stretch enough that you can use it without any tools or too much effort.