During the summer of 1985 -- after the Standard 4GF shape had already evolved into what we were riding all the time -- I tried a couple of further experiments. This time, altering the bottom texture of the nylon mats.
I covered the bottom of two mats I had laying around with urethane. The idea was to see if a smoother bottom would enhance the performance of the mats.
Two part liquid urethane was used, with two different durometer readings. The clear urethane I had on hand was hard. The red was very soft. The application on both mats came out about the same, but you can see the minor thickness variations of the red urethane more clearly. (I used a combination of a squeegee and a paint brush to apply the urethane, which is pretty thick stuff even in the summer.)
Both mats surfed noticeably slower, and their inflation levels were much touchier to get right on any given day. And, both mats exhibited less glide. Presumably, the reasons was because the mats were stiffer and wouldn't relax and conform as easily when you let them flatten out. Plus they sometimes had to be ridden firmer -- since the smoother bottom fabric didn't hold in as well -- and this slowed them even further.
The red-bottom mat was slightly better, which made sense since the red urethane was softer. But both were real turkeys!
One other test was conducted. I fine sanded the sheen off the clear-bottom mat with 320 W/D, to try and regain some of the "wetted-out" feeling the slick urethane bottom had removed. The mat was improved somewhat, but it was still a long ways from being as good as the taffeta-textured nylon.
After a couple of weeks riding theses mats, I took a stock 4GF nylon mat out and couldn't believe how well it worked, or how good it felt!