From Bushwalk Australia
Bubbles in the skin which can be painful, particularly if they burst, exposing the raw skin underneath. When bushwalking, blisters can form on the feet.
Essentially, blisters are caused by friction which is exacerbated by moisture. Friction is reduced by good fitting boots (most Australians wear their shoes a half size too small), appropriate lacing techniques, thin undersocks and where appropriate an extra friction reduction layer like tape (some tape however sheds its adhesive which then clogs up the heel of your socks, not desirable). Boot fit is a big issue for some people, particularly those with narrow and/or bony heels, if you struggle with boot fit you are probably better off with a composite boot rather than an all leather one, as they are a little more adjustable and forgiving.
Moisture reduction is really a function of wicking sweat away from the foot as quickly as possible, so moisture wicking socks or sock liners. Good sock choice is important. If you have really sweaty feet there are topical products available from the pharmacy for reducing perspiration but these would rarely be necessary - there is of course a much bigger risk of getting wet feet in Tassie from external sources.
If you do develop a blister the best treatment by far is a hydrocolloid stick on pad. These can be bought in most pharmacies in a variety of sizes and will stay in place for days. I keep a few different sizes in my walking first aid kit. Just stick them on over the blister. If the blister has shredded, it is a good idea to apply a bit of antiseptic first.
(information courtesy of bluewombat)