It is important to wear breathable undergarments, especially during warm and humid weathers to ensure that excessive moisture and heat can escape; otherwise it could lead to a conducive environment for the yeast fungi to breed, leading to vaginal thrush.
The breathability of an undergarment is based on two important factors. Firstly, the type of fabric used (e.g. cotton, polyester, nylon, etc.) as different fabrics have different breathability ratings. Secondly, the way it is woven into the finished product (e.g. an open-weave polyester netting will allow more airflow compared to a heavy tightly-woven fabric made from thick cotton yarns) is also an important determinant in an undergarment's breathability.
Properties of Fabrics
Lets understand the desirable properties of some of these materials that are commonly used in the making of undergarments so that we can make more informed decisions when purchasing them:
Cotton: Feels soft on skin, breathable
Polyester: Durable, resistant to shrinking/stretching/creasing, moisture wicking
Nylon: Durable, resistant to creasing, elastic, moisture wicking
Spandex (aka Lycra or Elastane): Durable, very elastic
If we are just purely comparing a fabric's innate breathability properties, cotton is more superior to polyester, followed by nylon and spandex.
In my opinion, you can never go wrong with 100% cotton for everyday use. For outdoor activities with lots of perspiration involved, avoid 100% polyester, nylon or spandex as they’re not very breathable. Instead, go for blended materials, such as polyester-cotton, which will give you the best of both worlds.
Final Tip: Check the materials of your yoga pants!