If properly cared for, your microfiber cloths will last ages. This is what I do to keep them cleaning better for longer, I gather them all together soak them for 30 mins in hot water with white vinegar. The white vinegar will deodorise and disinfect them. When I have enough for a load wash as normal. Make sure you do not add bleach or fabric conditioner, bleach will erode them and split the fibres and fabric conditioner will clog them up making them less absorbent when cleaning. They do dry pret