Rowell Abogado is correct in his answer. F254 can also be charred with sulfuric acid. The GF254 may show slightly different selectivity than F254, too. This is important if transferring methods to normal phase chromatography or if another person does the TLC on the same compounds.

Agreed that GF 254 plates contain Gypsum binder unlike F254 plates. Both GF 254 and F254 plates absorbances are at 254 nm, but GF254 plates fluoresce more under UV lamp than the F254 plates dues to the presence of gypsum binder