Wash-in laundry bags are small mesh or netting bags with zippers or drawstrings that you use to store delicates while doing laundry (to enable water and detergent to pass through).
Although they are typically used for undergarments or smaller-sized clothes, you can use them for almost anything—you don't have to limit them to things you'd keep in your underwear drawer, as they come in various sizes. Mesh washing bags are primarily used to protect delicate clothing while being washed, particularly if you have a mixed laundry load.
Portable laundry bags, on the other hand, are more of a storage option when traveling. You can use these bags to store the dirty laundry from trips. In addition, these bags are waterproof and odor-proof.