Tip: You can waterproof any fabric, be it shoes, jackets, or bed sheets(?).
You will need to mix naphtha, which can be found in the paint thinners area of any hardware store used to thin oils and plastics, with hardware store 100% silicone bathroom caulk.
Its a mix ratio of 1:5, 1 part silicone, 5 part naphtha, mixed in a plastic/glass tub until all the silicone is dissolved. You can then paint on the mix onto your fabric/clothing and the silicone will adhere to it.

Be sure to wear gloves and a respirator, or work outside as naphtha can harm your lungs. Have your fabric dry in the garage or outside on the balcony.