@Jazzy_girl as mentioned ^^^^^ PET bottles ARE stiffer than LDPE. I use both, for different purposes. I use the stiffer PET for long storage of juice and flavorings. I use the softer LDPE for testers, general vaping, and shipping, etc.
For my Nicotine which I store in the freezer, I break down my 500ml and 1L bottles into smaller 30ml/60ml amber glass:
For my larger 120ml/+ long steepers or for sale/shipping I use black PET with twist tops from SKS Bottles: (as mentioned above)
For testers, I don't waste money on expensive labels and just use Dots:
For anything I sell, I use nice B/W labels on 1.17" tape using the QL710W Wireless Labeler:
I shrink many of my bottles and have had VERY mixed results with the shrink bands on Amazon (the light blue ones), and ended up using the (clear/yellow) style from KKEMC:
Ultimately glass is ALWAYS the best container, but it's not always convenient. Different plastics will resist chemicals more or less than others, others are softer, easier to use but won't stand up as long vs. chemicals, etc.