Over the past half year, face masks have become a feature of day-to-day life, but not all face coverings are created equal and some can even be improved after they are purchased.

In general, when picking a mask, consumers can chose from two basic choices: A reusable-fabric masks or a single-use mask. 

Single-use masks can be expensive. In the UK, a single medical mask costs around $0.57. If a person were to use a mask every day for a year, the bill would add up to around $209.

By comparison, around $6 will buy a single reusable mask that can be worn multiple times. Some fabric masks can provide similar protection to a medical mask for most people outside the high-risk population. 

But there are a lot of different options for reusable masks, so how can a consumer find the most reliable one? 

Which?, a UK organization that advocates for customer information, tested 15 reusable masks in a study to determine which was the safest and why. 

And the differences between masks were quite remarkable: some filtered out 99 percent of particles, but others managed just 7 percent. 

Most people know that reusable masks should be washed after use to protect the wearer.

However, not only does each wash prevent COVID-19 from sticking around, it also improves the mask's ability to block particles.

"Almost all the face coverings we tested proved more effective at filtering particles after five hot washes, due to the fibers compressing," the study stated. 

This is because the fibers shrink on a micro level from the hot water when the mask is washed, which also means that the masks won't shrink after multiple washes. 

When shopping for a mask, look for it to contain two or three layers of cotton fabric, with three layers more often than not being the most effective. 

However, that doesn't mean that a two-layer mask would not be adequate protection against the virus.

A mask that has a disposable insert in the middle was the most effective face covering, according to the study. And this type of mask was able to protect the wearer from 95 percent of particles.

And a consumer doesn't have to buy an expensive disposable material to replace that insert. A simple paper tissue passed the study's filter test. 

Entirely understandably, customers tend to seek protection as the most important factor in a mask – but breathability isn't far behind. 

However, here the study has some bad news: more breathable masks tend to be less effective than a mask that sacrifices some comfort for effectiveness.

Even then, if a mask makes it too difficult to breathe it can actually decrease its effectiveness – because the covering can quickly become damp from condensation from the wearer's breath. 

In general, a damp mask is far less effective than a dry mask. So consumers have to strike a balance, seeking masks that are perhaps slightly uncomfortable but therefore safe, yet breathable enough that they don't reduce its protectiveness.

But the study added: "While some masks were more breathable than others, none were seriously difficult to get air through.

"So, if you are willing to sacrifice some level of comfort for higher filtration, you could opt for one of the less breathable options."

In addition, the study also pointed to some failings in the mask market – one example being the lack of a diversity of masks that would not fog the glasses of people that need corrective lenses.