People purchase table pads to protect their furniture from various types of damage. Table pads protect furniture from nicks and scratches, from water damage, and from heat damage. All table pads do a good job with the first two. Nicks and scratches are prevented with virtually any thickness of the padding, and water damage is prevented because the top layers of pads are made of a water-proof material. Heat protection, however, is another issue.
Most table pads are made with three basic layers--a vinyl top, a felt bottom, and an insulation layer between. The thickness of the insulation layer determines how much heat protection your table will have. Most table pads come with between a quarter inch and three quarters of an inch of insulating material. Approximately a half inch of material is enough to protect a surface from temperatures reaching 500 to 600 degrees.
However, note that although your table might be protected, the table pad itself can easily be ruined by extreme heat. The insulation layer might protect your table from a 500-600 degree cast iron pan taken right out of the oven, but the vinyl top layer will most probably burn or melt. Then, once that happens, although your table would still not be affected, your pad would no longer be water-proof, and the bottom of your pot might be ruined without a thorough cleaning with lots of elbow grease.
So, although table pad manufacturers tell you how your table will be protected at high temperatures, remember that your table pad itself might be destroyed. therefore, always place your pots on trivets/hot plates, even if you use a table pad. Table pads protect your table from accidental spills and nicks, but are not indestructible themselves.
Enjoy your dining room table for years to come. Purchase a good quality table pad and use it wisely.