My coroplast is 4mm thick. The 2mm is definitely too thin to build a cage although if you read the posts from (oh I can't remember - was it cornhill???) he makes an insert to lift out and remove the soiled bedding. 2mm might be good for that because it's more flexible and maybe you could even roll it up. I use newspaper sheets as my inner layer and they roll them up with the soiled bedding inside and toss. The 6mm I think is not necessary although it would probably work well for things like lofts and then you wouldn't need any other support under it.