Filtration
Filtration determines the size and number of particles there will be in the air when it is exhausted out of the vacuum. This does not have a bearing on how much dust or dirt the vacuum sucks up. Filtration is a feature of great importance to asthma sufferers and those with dust allergies. There are three basic types of filtration to choose from, standard, S-class/HEPA and lifetime filtration.
Standard filtration is found on less expensive models and is generally not suited to allergy sufferers. If you do decide to go for a vacuum cleaner with standard filtration, make sure you look for one with more than one filtration level. If a cleaner features microfiltration, this is standard filtration with at least 4 levels. (6 better still)
S-class and HEPA filtration is specifically designed to reduce the number of microscopic allergens emitted after vacuuming. The result is a cleaner outflow of air that is safer for those with asthma and similar problems, to breathe in. S-class is the name of the standard adhered to by vacuum cleaner manufacturers to achieve this aim, and HEPA (High Efficiency Particulate Air) filters are the technology most models of this type feature.
The above two methods of filtration will require a change of filter after a certain length of time. Lifetime filters, on the other hand, do not need replacing. They are guaranteed to filter the in-coming air throughout the life of the vacuum. Some S-class/HEPA filters are also Lifetime filters, but models featuring this type of filtration are usually more expensive
