Tbh it’s been said above. It’s mainly humidity change and part of that is due to our body, breath, and what moisture is on clothes and shoes. ( rain)
If the car is still fogging daily without being used then it’s likely there is a small amount of water ingress somewhere.

Shouldn’t be happening to you lot with new and year old cars.
I’d be off to Seat for a chat.

My car as a mk1 is prone to FLOOD at every given opportunity possible, from multiple points.
According to Morgan ,
a little water ingress means you’re a definate enthusiast.


Badger5 Custom Map + TIP,
3” Sustem, FMIC, Bosh 550’s,
BC Coilovers, ARB’s +loads more.
 
Bought a Pingi dehumidifier and it was gone in a couple of days, would recommend one! Easy to recharge them by microwaving them too.

Another fan of the Pingi dehumidfier here. Bought one for the misses and her foggy Astra GTC which worked wonders @ cutting down condensation during the colder months.
 
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Having the same issue (2018 Cupra 300 ST) when the aircon speed is set to low or automatic, have to raise the aircon speed to clear it up. Happens most in damp weather conditions ofcourse, but its still annoying as my previous mk7 GTI didnt do that at all. Guess the seals from the Spain didnt came so well done :O
 
I have a tub of Silica desiccant on the back seat during winter. The type that changes colour as it absorbs moisture and can be dried out in an oven. I leave a few tubs around the car if it wont be used for a few days.
 
When was the pollen filter last changed? As above leave the air con on year round, more fuel is used having an open window.
As already stated, the main cause of the windows fogging up are the pollen filter being damp and needing replaced. A leak in the car, check the carpets for damp. Your air con should also sort it out, but when was it last re-gassed.