Physical blowing agents are substances used to create foam by generating gas when heated or under pressure. They are commonly used in the production of materials like polyurethane foam and polystyrene foam. These agents can be gases or liquids that vaporize at certain temperatures, leading to the formation of bubbles within the material. These blowing agents are preferred for their environmental benefits, as many are non-toxic and have low global warming potential. Examples include carbon dioxide and nitrogen, which are often used in various applications, including insulation and packaging, to improve thermal performance and reduce weight.