Blueberry Flavor Concentrate for your DIY E-Liquids. Simply add Vegetable Glycerin (VG) or Propylene Glycol (PG) to your E-Liquid Concentrate, to make your own E-liquids. The E-Liquid Concentrate is Propylene Glycol (PG) Based. All ingredients are of a Pharmaceutical Grade. ALL DIY E-Liquids Concentrates are manufactured and bottled in the United Kingdom. This product is not to be vaped neat.