Nikwax Tent & Gear Solarproof used on pants or other fabrics ?

It should be fine. I soaked up excess spray when I sprayed my tent with my OR liner gloves and they are just fine, with the benefit of being water resistant now. In pretty sure if it doesn't harm synthetic tent fabrics it should be fine for synthetic clothes.

Thank you for your answer.

Did you notice if the gloves became stiffer, or had some sort of waxy residue n them after that ?

Regards
Mihai

No residue at all. They're black gloves too, so any residue would be noticeable, but I did not see any and the gloves did not feel any different.

If you're worried, try it on something expendable first.

I've also used wash in nikwax in a spray bottle thinned half and half with water and sprayed my clothes successfully so I don't believe you'll have any problems using the solar proof on clothing.