I used to be the owner of the #1 rated yoga mat company on Amazon. My company was called Tomuno.
I am NO LONGER in the yoga mat business so I hope I can provide an unbiased answer?
I am VERY glad you asked this question because I spent many years thinking about it.
I am hopeful my answer for yoga mats is applicable to “fitness exercise mats” in general. Typically they are made in the same factories.
If you prefer not to read what I wrote below, I also for fun created a “Yoga Mat Chooser Quiz” which will help you find the right mat without doing all the reading below. It offers videos. Here is the link:
Your Question: What are possible differences between cheap and expensive mats?
The three major raw material types that make up the vast majority of yoga mats in the wild are: PVC, TPE, and natural rubber. There are also cork mats, jute mats, etc. but these mats have less of a statistical track record and as such are harder to reliably score against the following criteria…
Yoga mats can be scored on several criteria:
Grip: How well does it prevent slipping if the user’s hands and feet get sweaty. In descending order of performance: rubber is grippier than TPE which is grippier than PVC (in general).
Cushion: How well does the mat prevent pain if the user has nerve issues or sensitivity in their joints, e.g., knees.
In terms of cushion, thickness is not important. Density is. A 5 mm TPE mat will not provide the same cushion as a 5 mm rubber mat because a rubber mat is much denser and hence provides much more cushion per mm of mat.
Weight: How heavy is the mat? If you walk to your yoga studio with the mat, yogis typically want a lighter mat. But if the yoga mat just sits at home heavier if fine. Heavy mats tend to perform better at a high level. In terms of weight, rubber is a lot heavier than TPE and PVC.
Compatibility with skin moisturizers, essential oil based mat cleaners, other lipids. Some mats are ‘closed cell’ meaning their surface has no pores and is smooth. Hence oils, sweat, liquids just bead and pour off the mat. Other mats are ‘open cell’ meaning they are literally like sponges. These mats soak up oils and moisturizers. The problem here is if you want a grippy mat and then put essential oils on it the oils will build up INSIDE the mat and create slipperiness. Some essential oils, for example, are also used as massage oils to create lubrication and slipperiness during massages. If these oils are used to CREATE slipperiness during massages they will also create slipperiness on yoga mats.
Rubber is open-cell in general. TPE and PVC are closed cell in general. But there are exceptions so it is important to read the label.
Durability. Some mats only last a year on average, e,g., yoga mats made of natural rubber. Other mats will last practically forever, e.g., plastic PVC mats. Rubber performs quite well but it is very expensive. Many yogis rightfully do not want to spend that kind of money each year on a new mat like they have to buying new rubber-soled running sneakers every year.
Ease of maintenance. Some mats are very easy to take care of, e.g., PVC mats. You don’t need to read a booklet to learn how to maintain them. Other mats do require quite a bit of reading to learn how to take care of them. For example, natural rubber mats cannot be left in the sun, they cannot be left in a hot car trunk, the cleaning process is a bit complex, etc. If you aren’t eager to invest the time in learning these things sometimes ‘easy to maintain’ is the way to go with your yoga mat selection…
To help you choose what type of mat (PVC, TPE, natural rubber) is best for you, a yoga studio owner would typically ask you about the SIX criteria listed above to find out your relative preferences and then recommend the yoga mat raw material that works best specifically for you.
“Raw material” is more important than “brand” when it comes to yoga mats in general.