What is the Best Sound Isolation underlayment for ceramic tiles?

There are several sound isolation underlayment available for ceramic tile flooring.
One of them is this...
http://www.laticrete.com/Homeowners/Products/Underlayments/tabid/218/Default.aspx


It is important to have noise reduction especially for second floor installation.

I understand that there are ratings for noise reduction like Impact Noise Rating (INR), Sound Transmission Class (STC), Impact Insulation Class...
I understand, the higher the number, the better it is.

What is the Best Sound Isolation underlayment available for ceramic tile flooring?

Not sure about best, but check out www.custombuildingproducts.com for EasyMat. It comes in various thicknesses...the thicker, the more sound isolation. Noble company also makes some. I've not used any of them, so I can't say.

There is no best. All are good. Some dampen more sound and cost more money.

To stay with synthetics, search on soundproofing membranes. Cerazorb and Acousti-tech are two that are made specifically for the highest standards, and they cost it. They are made felt-like, with a lot of trapped air. At the low end, thinner membranes are made like neoprene, with complex strand molecules that absorb some energy instead of transmitting it.

Cork is the original membrane and it still works. All natural, it has 14,000,000 little air pocket cells in a cubic inch. This is what modern (synthetic) foams are modelled after. It does not rot in a cement-tile sandwich, at least not unless your entire wood frame house begins to rot.

david