The Coopers DIY Beer Kit contains thirty 740ml PET bottles. These bottles are also widely available as a separate item (in boxes of fifteen). PET stands for polyethylene terephthalate, which is the same plastic used to make soft drink (soda pop) bottles. Since 2000, Coopers has included PET bottles with the starter kits (initially the Micro-Brew Kit and now the DIY Beer Kit) rather than the traditional crown seals and capper because it was becoming increasingly difficult for new brewers to obtain sturdy crown seal bottles. Today, most commercial beer is packaged in single use glass bottles, which are too thin to stand up to the rigours of continual washing and capping. These bottles carry the words "no refill" embossed on the glass. The majority of PET bottles are subtly porous and a beverage held in PET will eventually go flat. However, Coopers PET bottles have a nylon barrier, reducing the the rate of ingress of oxygen and the loss of CO2 for up to 18 months. The re-usable caps have a tamper evident collar that breaks off after the first use. This does not affect the airtight seal. When the caps eventually wear out, replacement caps can be purchased separately. Note: PET is temperature-sensitive and should not be cleaned using hot water. A beer, such as an Imperial Stout, intended to be aged for 2 years or more, should be bottled into sturdy glass designed for re-use. With this in mind, Coopers also produce Original Pale Ale, Sparkling Ale and Best Extra Stout beverages in sturdy 750ml glass bottles. These bottles have a lip designed for a prise-off crown seal and weigh a formidable 560g empty! They are an excellent option for brewers and sauce makers, alike.