There's little or no real science involved. We already make materials that are all one molecule for all practical purposes (breaking them involves breaking bonds within molecules, not merely separating intact molecules) and while they are very strong by ordinary standards, those materials are nothing like GP hulls.
The most detailed discussion of a GP hull is in the story "Flatlander" where Beowulf Schaeffer and B/r/u/c/e/ P/e/l/z/ Gregory Pelton are asked to explore a mystery planet by the Outsiders. As they approach the planet, they talk about the GP hull: "Bey, can anything get through a General Products Hull?" "Light, like a laser beam. Gravity, like tides crushing you into the nose of a ship when you get too close to a neutron star. Impact won't harm the hull, but it'll kill what's inside." (In another story it's mentioned that the only light that passes through the hull is that used for vision by one of races the Puppeteers sell GP hulls to.)
As they approach the planet, the GP hull suddenly disintegrates. They limp back to civilization and General Products explains: The planet was made of anti-matter, and "A General Products hull is an artificially generated molecule with inter-atomic bonds artificially strengthened by a small power plant. The strengthened molecular bonds are proof against any kind of impact, and heat into the hundreds of thousands of degrees. But when enough of the atoms had been obliterated by antimatter explosions, the molecule naturally fell apart."
So there you have it: Instead of the hull being made of handwavium, it is ordinary matter that is turned into artificial unobtanium by means of a small power plant. There's really nothing more you can say about the technology. OTOH, given the magic, you can speak about the consequences.
GP hull material can't be deformed -- it's very, very hard -- because the individual bonds are very, very strong, yielding an extremely rigid material. Deformation of any sort begins with some bonds being stretched and others being compressed. If the bonds are not deformable or breakable, the material becomes enormously rigid and hard and you get the effect mention in the story: An impact pushes the whole hull without breaking it and the contents thud at high speed against the invulnerable hull and are crushed.
The hull being impervious to electromagnetic radiation other than light is much harder to understand. There are two ways to exclude EMR: reflection and absorption. To reflect EMR, the hull would need either to be conductive -- metals reflect light well, and mirrors have a metal coating -- or have a carefully constructed impedance mismatch. The latter is hard to do across wide frequency ranges and it's not obvious how the GP hull would do this well without it having something else going on than just the artificially strengthened bonds.
Absorption means that the EMR's photons interact with the substance's electrons and energize them. That's one of the things that the GP hull's magic power plant must prevent, so it's hard to see how absorption would stop EMR.
So the artificial rigidity of the bonds (which are made of electrons, after all) which does a nice job of giving the hull rigidity, would also appear to make it transparent to most frequencies of EM radiation! (Even using the SF physics of the story.)