I bought some glass bottles and silently forgave myself for letting Sam chew on oodles and oodles of bad plastic during his short life.
The knit comes from small scraps I got ages ago, and both sizes of bottles just need one size of tube, since you can just double back the fabric on itself for the small ones. It helps keep things nice and snug on the little ones, too. So. Now no knocking into each other in the bag, no condensation or weird dribbling, and no slipping out of big brother's hands. Unless they are thrown, which would not surprise me at all.