Carpet underlay, also known as carpet padding or carpet cushion, is placed under carpet in order to protect carpet from premature wear, while also increasing the comfort of the carpet. Carpet underlay comes in several materials, including waffle underlay, urethane and flat rubber. While the cleaning requirements vary depending on the material, you can implement several general cleaning techniques to maintain the quality of your underlay and surface carpet.
Remove the surface carpet. If it is not damaged or dirty, move it to another room so you can reinstall it after you finish cleaning the underlay.
Vacuum any lose dirt and debris from the underlay. If possible, opt for a vacuum with a HEPA filter so that debris doesn't blow into the surrounding air.
Put on kitchen gloves or other protective rubber gloves.
Soak a soft cloth in oxygen bleach and wring it out over a sink or bucket so that the cloth is moist, but will not cause bleach to pool on any surface it touches. Gently dab any stained areas of the carpet pad, such as where pet urine stains leaked through the surface carpet. Do not add bleach directly to the carpet pad and do not drag the bleach through a large area of the pad. Simple dabbing should remove the stain and smell.
Place an industrial vacuum and dehumidifier in the room and wait for the carpet underlay to dry.
If grey or blackwater -- contaminated water -- or mould and mildew damages your carpet underlay immediately throw away the underlay and replace it. Failure to replace a water-damaged or moulded underlay could cause serious health issues, in addition to ruining your carpet and subfloor. Even if you thoroughly soak your underlay with sanitised water, if you are unable to dry the underlay quickly with an industrial fan you will need to replace the underlay.