These graphite flakes have had an expansion agent inserted between the individual layers of carbon atoms (aka intercalant). When heated to above 150°C the expansion agent starts to produce gases that cause the atomic layers to separate. The flakes expand to several hundred times their original thickness and form an effective insulating char layer that protects the underlying substrate from further heat degradation and also reduces the creation and release of toxic gases.
It is used as a fire-retardant additive in plastics, foams, wood products, textiles, putties, and coatings. It is also the active ingredient in firestop products such as intumescent foam. Se for example this Intumescent Foam
The graphite can expand to a volume of 250 cm³/g and reaches full expansion at a temperature of close to 1000°C. Different variants have different expansion temperatures and expansion levels.
Create plastic Christmas decorations that don't catch fire.
Heat the sample with a lighter or a gas torch to observe the expansion.
You get 10 g of expandable graphite.