Celotex and Kingspan are leading insulation brands, but they differ in their offerings. Celotex specialises in PIR (polyisocyanurate) insulation boards, known for excellent thermal performance and moisture resistance. Kingspan, on the other hand, offers both PIR and phenolic insulation. Their Kooltherm range, made from phenolic foam, provides superior thermal performance and fire resistance, while their Therma range is similar to Celotex's PIR boards. The choice between them depends on your specific needs, such as thermal efficiency, fire safety, and budget.