When you need greater capacity, the Silo is the ticket. It is leak proof and easily slides into standard packs and backpack side pockets. It is very durable and has the standard 63mm Loop-Top cap. The neck configuration works with most major water purifiers and filters. Sustain bottles are made with material derived from 50% plastic waste. Each bottle is created from resin powered by next generation recycling technology that transforms plastic destined for landfills into high-performance bottles.