Britax USA manufactures a wide variety of products for child passenger safety including car seats such as Britax Marathon. The car seat cover is a sewn fabric material wrapped around an energy-absorbing foam and a molded car seat shell. Cleaning the cover once removed only requires a mild washing and drying process. The only difficulty you might face occurs when attempting to remove the cover from the seat as the harness, shoulder straps, buckles and other related pieces thread through the cover requiring disassembly.
Loosen the harness and shoulder straps. Lift the adjuster lever with one hand while pulling the shoulder straps toward you with the other. Reach behind the seat and remove the straps from the harness yoke. Reach to the front and pull the straps through the slots in the cover.
Remove the harness buckle. Recline the seat back. Pull the metal buckle retainer under the seat and then fit its shorter side through the slots in the shell and cover.
Pull out the remaining pieces that thread through the cover such as the bottom harness straps and chest pad.
Take the cover off the foam backing and shell.
Wash the cover by hand in a basin or sink filled with cold, soapy water and then rinse.
Dry the cover. Lay a soft, lint-free towel on a flat surface. Squeeze any excess rinse water gently from the cover by hand and then place the cover on the towel to air-dry.
Return the cover to the car seat and then reassemble the pieces.
To remove additional excess water, wrap the cover in a towel and squeeze to force excess water from the cover into the towel. If you have difficulty removing a stain on your Marathon cover, soak the cover in the cold water for 10 minutes and then gently scrub at the stain with a soft-bristled brush to dislodge any caked-on particles.
Never disassemble the harness or remove the buckle tongues as only Britax can reassemble the harness and/or tongues to function as intended for regular use and safety. Never wash your Marathon car seat cover in a washing machine or dry it in a dryer as doing so can damage the cover. In addition, washing the cover in chlorine bleach and/or ironing it can also result in damage.