Unless it's made of a non-porous material like rubber, no jacket is 100% waterproof. Since rubber is non-porous, it's also not very breathable, so you may find gear made of rubber sacrifices a little bit of 'give' for function (think a sturdy waterproof rain jacket vs. the water-resistant sneakers you run in.)

What is a rubberised jacket?

“Basically, rubber rainwear contains a woven textile with a coated front side in a rubberized material, which is a classic waterproof combination,” Hesselager and Lotko explained via email. ... The brand Stutterheim creates similarly classic-looking jackets, though it uses a PVC coating.

How can you tell if a jacket is waterproof?

Waterproof ratings are measured in millimetres using a Hydrostatic Head test. In a Hydrostatic Head test, the fabric is pulled tight under a 1 inch diameter sealed tube of water. This is then observed over 24 hours to ascertain how many millimetres of water the fabric can withstand before it soaks through.