There are 2 different types of Fire Retardant that are useful for protecting your home and property from a wildfire:
Type #1 - Short Term Fire Blocking Gels
Short Term Fire Blocking Gels are great for protecting structures, particularly the walls and eaves of a structure. The Fire Blocking Gel is applied with either a garden hose applicator, pressure washer applicator, or special eductor applicator that screws onto the end of a 1.5" Fire Hose. All the Fire Gels do a reasonably good job of clinging onto the side of a house withstanding flames and high heat that are typical in a wildfire. There's a bunch of videos on the internet that you can watch of how a board coated with fire blocking gel vs. an untreated board perform when lit on fire.
Barricade Fire Gel, Thermo Gel, and Ember Bloc are all examples of brands of short term fire blocking gels. They last anywhere from 6 - 18 hours depending on the conditions and whether the gel is rehydrated by re-misting it with water. They have all been proven to be really effective, but only if applied right before the wildfire approaches the structure that you coated.
Type #2 - Long Term Fire Retardant
Long Term Fire Retardant are essential in saving your home from a wildfire. The long term fire retardant is a liquid that is mixed with water and sprayed around the perimeter of your property using a pump sprayer. It gets sprayed on the vegetation, mulch, log piles and other fuel sources all around your house and creates a fire break that lasts many months. Phos-Chek is an example of a long term fire retardant that has proven to save many homes over the years.
Summary: If you live in a wildfire prone area, you need to get both. Have some short term fire retardant gel on hand (i.e. Barricade Fire Gel) and practice spraying it on the exterior walls and eves of your house so you are proficient applying it right before you evacuate before a wildfire event. Have some long term fire retardant on hand too (i.e. Phos-Chek) and practice mixing it and spraying it with a backpack pump sprayer.
Disclaimer: None of these solutions talked about in this article replace the need for constantly maintaining defensible space all year long around your property. It's always recommended that you ensure your personal safety above anything else, adhering to your local fire firefighter's instructions and evacuation orders.