If you are fortunate enough to have a pool then you have no doubt contemplated or bought outdoor fabrics. Many people are confused about the properties of the fabrics they need in these environments; intuitively you feel that you need something that is waterproof.
Let’s look at cushions.
Essentially if a fabric is waterproof it has the same water characteristics as plastic. It means it is totally impervious to water, i.e. water will not penetrate it (leaving aside the seams). You really don’t want that for a poolside fabric. What if it is pin-pricked and what happens to the air inside when you sit on it? That won’t be able to get out either.
Most people buying outdoor cushions accept that they will leave the cushions out overnight by mistake a few times (so condensation will be an issue), most accept too that the cushions will be sat on by people who could be wet.
It is important that you buy water resistant fabric not a waterproof fabric.
Water resistant fabric is treated with a finish that is resistant but not impervious to penetration by water. So, for example, rainwater will form drops on the surface. If you then rub the water it will penetrate the fabric BUT it will also dry out more quickly AND it will allow air to pass through it. If you leave a cushion made out of this overnight occasionally it will be fine.
KOTHEA sells fabrics made from solution dyed yarns that are resistant to water and stains.