Glass Roll On Bottles With Metal Glasses Best Quality 10ml (1/3oz) Cobalt Blue Glass -For Aromatherapy, Essential Oils, Perfumes and Lip Balms - White These metal balls have a perfect tight fit that won't ever leak. With the bottle inverted, the weight of the steel ball creates a seal preventing oil release. A quick shake allows the release of the oil for a smooth and even application every time Certain oils & chemicals do not interact well with cheap plastic balls and possibly ruin the rolling mechanism. Stainless steel roller balls do not erode and will continue to roll on smoothly every time Our luxurious glass bottles are not painted and will not scratch easily. Elegant cobalt blue frosted bottles have a deep rich and dark color to prevent light damage to sensitive oils. Refillable so you can use over and over again,Convienient size so you can take anywhere with you.