There are two different types of spa filters that are largely used in modern portable spas and swim spas: pleated spa pool filters and micron spa filters.
Pleated spa pool filters:
Pleated spa filters are the most common type of filters and are typically good for filtering out particulates 20 microns or larger.
As the name suggests pleated filter cartridges are made from pleated filter material known as media.
Why is it pleated you might ask? The pleats dramatically increase the surface area of the spa filter which increases the efficiency and reduces the overall size requirement.
Micron spa filters are either used alone or in conjunction with pleated filters. Micron filters use a different "spun" style of filter media and typically are good to 5 microns so they are ideal for clarifying water.
The advantage of micron filters such as the Purezone spa filters, is that they save money by reducing the amount of spa chemicals required to maintain water clarity. As with everything not all filter media is made the same and the quickest way some manufactures cut costs is by lowering the quality of the filter media being used. Non factory authorized spa filters can be made from filter media that breaks down rapidly and does not clean out well causing it to become clogged an unusable much quicker than the higher quality spa filters.
One more important aspect of spa filter construction to note is how the end caps are fixed to the filter media. Another way certain manufactures of low quality filters save money is to use lower quality process to attach the filter caps onto the filter media. This often causes the filter to come apart at the end caps very early in their life span.
Take away: Replacement spa filters come in two main types, pleated and micron. Make sure to purchase filters from an authorized, reputable supplier that offers a guarantee. Poorly made filters can fail and cause damage to your spa.