What to seal chipboard flooring with to protect against dirt

[clc.sheff]

Question as title really.

Have re-floored out all my attick and put a drop-down ladder in but as the area will be used quite a lot I thought it would get grubby fairly quickly.

I have used full size, green (waterproof ) chipboard.

I'm thinking either a coat or two of PVA, OR, polyeurathane varnish but don't know which one to use or indeed if I should be using something else?

I think I would prefer the surface to remain natural coloured rather than painting it white

I'm also not sure if the boards need to allow moisture to pass through them? i.e. is it a bad idea to varnish.

If PVA is the right way to go I have waterproof and normal stuff and again could do with knowing which one.

Rang a couple of paint shops and was given completely contradictory advice so just a little confused and would love to get cracking so I can put all my boxes back up in the attick

Any help would be greatly appreciated.

Thankyou for any replies. Clc.sheff