Synthetic materials, especially polyester, can quickly obtain a bad smell if they are in contact with sweat and not washed instantly after.
So don’t leave your washing bin lying to long, to save your products from bad smells.

If you wash your synthetic materials at too high temperatures, you risk they’ll be permanently wrinkled. Pay special attention to the care label on synthetic materials.
Acrylic for example cannot take higher temperatures than 40 degrees.

Most synthetic materials dry easily. Take advantage of that and hang them up to dry outside.

Synthetic materials release microplastic when being washed.
Therefore, always use a laundry bag to retain the microplastic.

Synthetic materials do have a tendency to shrink during wash.
Get your product back to the original shape, by ironing while still damp.