This is achieved through the application of a protective film that binds around the carpet or upholstery fibres, making it easier to soak up spills before they cause permanent damage, and generally making your carpet or upholstery more resilient to wear.
For this reason, carpet protection is commonly applied after manufacture, helping to protect carpets in transit and throughout the period of any warantee. However, protection does wear off over time and should be reapplied as necessary.