These beautiful 1 oz, 30ml glass bottles are a handy way to apply essential oils, blends, and massage oils to the skin-simply roll them on as needed. These 1 fl oz (30 ml) Roll-on applicator bottles have a Large Resin roller ball, and the bottles are sturdy glass. Please note that some essential oils can interact poorly with plastic, and it is important to test any blends before filling a large number of bottles You need to test any blends. Certain oils, like clove, black pepper, myrrh, mints, tea tree, lavender, citrus or frankincense can dissolve plastics. (the housing which holds the balls is plastic) And, very lubricating carrier oils, like coconut fractionated oils, cause the roller to get so lubricated, that they pop out of the housing. (this is only a partial list; this is so of all rollerball bottles,not just ours) Essential oils are effective because they have chemical properties. It is those same properties which create chemical reactions with certain other ingredients/materials. It is a scientific fact that some oils dissolve plastics, and are not a good fit with roller ball bottles for this reason.