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What type of fabric / materials are the cusions made of?
its the liner of the cabin, think some type of synthetic fabric .thanks for trying to help
Some stains, like mold and mildew, are very hard if not impossible to remove all the way.
You can try a non-chlorine bleach, that's going to be about your best bet.
Only use it diluted at about 25%non chlorine bleach to 75%water
I have also had good luck with 409 with bleach in it (pre made and sold that way)
It will take a few applications but that should get most if not all of it out.
If these cushions have a removable cover (if you can remove the padding from the cover) you can try hand washing them also.