I was worried that the previous sentence was not in English, so I posted it again.
The size of the gel sheet is 25cm x 25cm x 2cm thick. I ran about 100km after seat improvement. It was so comfortable that I forgot about the seat when I was running. I think seat modification was a success. My weight is 62 kg.
I would be happy if it could be a reference for those who think that the R18 seat is solid.