The main difference between a foam and a fiberglass surfboard is in their strength. Fiberglass has many layers which give it increased durability without increasing weight significantly.
You need a foam blank, fiberglass and resin that's compatible with the blank, plus solvents, paints, cleaners...
In 1958, a shaper named Hobie Alter and a glasser named Grubby Clark perfected the polyurethane foam blank. In 1961 the two created a second company, Clark Foam, to make surfboard blanks. Soon thereafter, the surfboard was made from fiberglass, polyester resin and polyurethane foam.
There are a variety of surfboard constructions coming out now including epoxy, firewire, Solomon and many others but the traditional surfboard is a polyurethane blank and fiberglass. The polyurethane blank aka foam is shaped down to a specific shape then coated with a resin that is strengthened by fiberglass cloth.
Mainly a Foam Compound
a blank is basically the core of the surfboard, a big foam block that you shape into the board of your shape and desires.
It would depend on the construction of the craft, but as a general rule, the fiberglass boat will be heavier.
In the 1970's, a Man named Shane Steadman came up with the idea of a foam surfboard. His main goal was to make the surfboard safer to learn how to surf for beginners, and easier to travel with. After several attempts, he finally got it to work, and the foam board became a major hit!