Wife wants to replace the old floors with this new pergo timber craft waterproof stuff. I had a few flooring guys come look at the job and I was told I don’t need the fancy expensive underlayment and could use 30# roofing felt to save some money. They claimed it’s basically the same, adds as a padding and moister barrier. A little research seems it’s not uncommon, Ive just never heard of it I guess. I’m on a crawl space if that matters. Looks like 30# felt is about .062 thick so that’s around 1.5mm. Seems most underlayment is 1.5-2mm unless you pony up for the 3mm. Opinions?