There are many brands of stain protectors like stain guard, Teflon, guardsman, scotch guard etc in the professional market. Let’s see how they work actually.
Basically, all the protectors are deigned to adhere to the fabric. Either it be carpets or upholstery, they form a sort of soft coating. It will be more resilient too. It is manufactured to be soft because if it is a hard coating, then it will alter the texture a lot and it will make them feel hard like varnish. It has to be soft but it loses its effectiveness over time and with use. It does give good protection, no doubt about it!
The molecules of the protector bond to the surface of the fibres of the carpet and after they get dried fully, they stop lot of different liquids from staining the carpet almost permanently. It cannot stop every liquid but that does not mean it is waste to use it. It has to be applied effectively for it to work properly. Some type of liquids may bead up and come up to the surface again. This phenomenon will depend on the temperature, content and makeup of the carpet fibre. There are few instances where the protector is not applied properly but even then it will not bead up. The best example is a synthetic yarn in woven construction. There is a thing of interest here. The actual wear to fibre is reduced because the coating of the protector is worn out first before the actual fibre itself. It helps against premature wearing of carpets.
You get for what you pay! So never go for cheap ones. The ones which are costly will generally work fine. No one can ever apply a fantastic protector for a quite cheap price. If you get a really cheap quote, beware! You might be just paying them for spraying water instead of protector. It is always recommended that we use an effective product to keep carpets spic and span.