Re: How do they make fabric, couches, pajamas less flammable? What do they use?

Fire proof suits, e.g. for racing drivers can be made with flame resistant polymer fibres. You can read about one called "Nomex" at Dupont. The polymers have high melting points, and strong bonds which are not broken in favour of the formation of oxidation products (carbon dioxide and water)until high temeratures are reached.

Normal materials, e.g cotton, can be treated with a flame resistant polymer which is absorbed into the material. An example is Proban. Sometimes these only work until the material is washed, or their efficiency is reduced with each wash. Some are available in a spray can. The polymer chars on heating, forming an insulating layer of carbon which isn't penetrated by fire, at least not until the temperature becomes very high.

Other fire retardants (e.g. for plastics, wood) contain compounds that include phosphorus, nitrogen, antimony, chlorine, or boron, depending on the application and the material to be treated. These agents work in different ways. Some reduce the amount of burnable fuel vapors produced by the burning substance. Others release gases that do not burn, such as water vapor, to dilute the fuel vapors. Still others slow the rate of oxidation, thus reducing the rate at which energy is released and the amount of heat that is generated. As you suggest in your question, these agents are only retardants, they do not make things fire proof. If the house is on fire, your pyjamas will burn, but they are not likely to be the cause of the fire.