Aluminum-clad fused silica columns offer the same inert internal fused silica surface, but with an outer layer of aluminum instead of the standard polyimide normally found on GC capillary columns. Polyimide has an upper temperature limit of approximately 390°C before degradation occurs. By utilizing an aluminum outer layer, GC columns can extend the operating temperature range upwards to 440-450°C which is useful for high molecular weight applications.

The 400-5HT phase separates compounds according to boiling point, and is produced on 0.23mm ID aluminum-clad fused silica.  This allows for higher operating temperatures compared to the standard polyimide-clad fused silica columns.  The 400-5HT columns can be programmed up to 420-440°C and are well suited for high molecular weight applications such as crude oils and waxes.