Is spun polyester waterproof?

The following is an explanation of the water resistance of spun polyester:

I. Inherently not waterproof, but can resist splashes

▸ Ordinary spun polyester fabric:

Absorbs water like a sponge: The fiber structure is loose and porous, allowing rainwater to slowly seep in (similar to cotton fabric).
Resistance to light rain: Can only resist light rain splashes (5-10 minutes), but will become completely soaked in heavy rain.

▸ Comparison with waterproof fabrics:

II. Under what circumstances can it be temporarily waterproof?

▸ Surface treatment:

Coating treatment: A layer of glue is applied to the back (such as PVC, PU), which can block short-term rainfall (e.g., cheap umbrella fabric).
Waterproof spray: Forms a temporary water film after spraying (loses effectiveness after 3-5 washes), suitable for emergencies.

▸ Untreated spun polyester:

Used as curtains, it will absorb moisture; used for backpacks, items will get wet in the rain.

III. Precautions for daily use

Not suitable as rain gear: Don't expect a spun polyester jacket to act as a raincoat; it will definitely get soaked in moderate to heavy rain.
Damp and moldy: Difficult to dry after absorbing water, prolonged dampness easily leads to mold (especially shoe linings, sofa covers).
Risk of chemical residue: Waterproof coatings may contain irritating substances; those with sensitive skin should avoid using it close to the body.

IV. Alternative solutions when waterproofing is needed

Inexpensive option: Choose nylon taffeta fabric (lightweight and water-resistant, suitable for backpacks, tents).
Durable option: Choose polyester fabric with a PU coating (strong waterproofing, but a harder feel).
Natural option: Waxed canvas (cotton + wax layer, breathable and water-repellent).