[Bumpy]

In an ideal world drivers would be sonically if not physically isolated from the baffle.

Failing this, a quality gasket material becomes an option to present an acoustic block.

The obvious seem to be cork, foam or rubber, but in this age of new technologies are there any other material from which gaskets can be made?

[richidoo]

I've used this in my last 10 speaker builds. It is rubber foam, hollow, D shaped tube with self adhesive, 5/16" wide, 1/4" tall, 4 colors. I works great. Allow extra 1/16" depth in rabbet. Compresses easily, pushes back on speaker flange like a spring to make easy adjustment to achieve perfectly flush driver. Doesn't slack over time. Cheap. Adhesive sticks to bare wood. Foam never sticks to driver flange. Install it on the inside edge of the speaker hole, inside the mounting screws.
https://www.amazon.com/dp/B00FQ5A5RM
Also sold at local home improvement stores, usually in the brown color. Two strips of 17' per package.

[GeorgeAb]

I too, as said above, like the Frost King weatherseal products. I have used the 3/8" wide X 3/16's thick on a few projecsts. Easy to work with and have been happy with results.

[Jazzman53]

I use this gasket material: https://www.parts-express.com/Speaker-Gasketing-Tape-1-8-x-1-2-x-50-ft.-Roll-260-542

However; no gasket material can effectively isolate the driver from the baffle if the driver is attached with screws which transmit the vibration. 

To maximally isolate the driver from the baffle, you can just glue it on with silicone. 
1)  Set the driver 3/8" away from the baffle board using small spacers.
2) Fill the gap with RTV silicone and let is set up.
3) Remove the spacers and fill the gaps where the spacers were with RTV silicone, to complete the seal.

Now there are no hard connections to transmit the driver's vibrations into the baffle-- only the soft, dampening silicone.

The downside is that you would have to cut thru the silicone if ever wanted to replace the woofer. 

[FullRangeMan]

What are the sound effect intended on the panel:?

+ For a resonant panel use no gasket at all.
+ For a mid resonant panel use rubber gasket 2mm.
+ For a near full isolated panel use 5mm solid felt gasket.