Rugs, Carpets and Carpeting - Carpet Underpad Question

Hi Im no expert so I have no idea on this topic...Which carpet underpad (foam) is better?

5/16 or 7/16?

And would a 12mm super pad be a good investment for 35 oz carpet? Or 40oz carpet on the 5/16 or 7/16 pads?

IMO, the better the pad, the more you'll like the carpet - I buy the best I can.

Not to sound like a commercial, but we just had the carpet replaced in our living/dining/entryway areas over Christmas and opted for the Stainmaster pad. The difference over the old carpet and pad are phenomenal.

A quality carpet cushion will extend the life of carpet, especially in high traffic areas. Avoid too soft or too thick cushion. Cushion density is important--certainly not less than 6 lb/SF & 8 lb/SF better choice. Thickness should not be greater than 1/2" (3/8" preferred with berber). It is best to use the recommended cushion for your particular carpet selection as recommended by the manufacturer not the carpet showroom sales rep. Selecting the wrong cushion may void carpet warranties. The carpet dealer should look up the manufacturer's recommendations (remember these will be minimum recommendations) or call the manufacturer while you are standing there. Make sure you get what you paid for.

You want a firm and resilient cushion that will withstand wear and tear. Thinner and denser cushion is best for high traffic areas like stairs, hallways and rooms where there is much traffic. You want a cushion that can withstand traffic, keep carpet from looking matted and worn down, provide insulation, and reduce noise.

Hmmm...I have a general idea now, however...what is the difference between a:

5/16 foam vs 7/16 foam vs 12mm super pad?

What does 5/16 stand for? 5/16th of an inch??

5/16 wouild be the fraction of inches.
5/16 is close the afore mentioned 3/8 and 7/16 is pushing the 1/2 limit that was also metioned.....afore.

5/16 8-lb rebond cushion is usually sold for loop pile berber carpets, to keep the manufactures warranty. I would not exceed a 3/8" thickness and no less then an 8-lb rating, under a loop pile.

For cut pile tufted carpets, 7/16 is the limit for thickness to keep the manufacturers warranty. Most rebond cushion marked ½" is actually 7/16 and they up sell it for way more cost. 6-lb is the lowest density used with cut pile carpet and still keeping the manufacturers warranty.

since 7/16 is close to 1/2 an inch, is there a point to upgrading it to 12mm super pad?