Since you’re actually vaporizing the top layer of material as you’re engraving, the mark from a CO2 laser is permanent on textiles. How the material holds up during normal wear and tear depends on the strength of the fabric and the settings you used to create the mark.
Hearty fabrics, such as canvas, denim, and leather hold up well to normal use. Fleece is another material that holds up to washing and drying, provided the surface etch is light. Knit fabrics (like T-shirts) are typically thinner, stretchy, and less durable than woven fabrics. They can still be laser etched, but the mark needs to be very light so as to not diminish the structural integrity of the material.