Swore by 6lb pad for years, then a hallway job in Tulsa changed my tune
I used to think anything under 8lb was cutting corners until a homeowner on a slab in Tulsa asked me to match the feel of her old wool carpet, so I tried a 6lb pad and the seams laid flatter with zero callbacks in 7 months, which makes me wonder how many of you are still defaulting to the thick stuff out of habit.
Had the same thing happen on a rental turnover last spring, cheap berber going down over concrete and the 8lb I had stacked in the truck was just fighting me at every seam. Grabbed a 6lb roll from the shop and it laid down so much nicer, seams disappeared after a good stretch and rake. Tenant moved out 8 months later and not one wrinkle complaint, which I was not expecting on a slab. Now I keep both on hand and pick based on the carpet and the subfloor instead of just grabbing the thick stuff.