High Temperature Insulation
When you insulate the pipe work to and from the collector. Make sure you use insulation that will resist the high temperatures. The pipe work can reach very high temperatures and normal insulation is likely to melt. The flexible stainless-steel pipe comes pre insulated with high temperature insulation.
You can often buy cheap insulation at local building suppliers. This is OK on the cold water lines, but the insulation nearest the hot water out connection of the collector has a high chance of melting. If this is OK for you then you could use it but this can be a real headache to clean up and replace on the roof or in your roof space.
The flexible solar piping uses high temperature EPDM insulation that is designed not to melt under the solar temperatures.
Full specification of this flexible solar pipe and EPDM insulation can be found here.