What are the dimensions of the large bag?

31cm x 28 cm. I dont have it in inches, I'm from the Netherlands ;)

Has airport security ever forced you to remove your film from this bag and put it through the x-ray scanner again? concerned tsa might not allow this.

TSA's in my experience will ask you to empty the bag, so they can search it. You should really alert them of it beforehand, 'there is a photographic film protector bag in my luggage to protect my light sensitive film from radiation from the scanner and flying radiaton, it will not show on the scanner, you may search the bag manually' - in my experience they will be okay with it then.

Hello! do these bags protect film that is iso 400? what about 800? thank you!

Absolutely. The higher the ISO value, the more they need protection. Film gets more sensitive for radiation when its more light sensitive! I used it to carry around 1600 and 3200 iso film through Chernobyl. Airport security won't be able to see the contents so be ready for extra searching. It is best you mention it upfront.