The answer to your selected question is shown below.
An insulated roller garage door has a curtain which is made from individual sections of lath sections all joined together by various methods, depending on the manufacturer. When the curtain is fully rolled up and the door open the curtain sits at the top of the side guides and is rolled around a steel barrel which itself is held between 2 endplates either side.
These endplates are designed with a lip on them which can take in most cases a half or full hood aluminium cover to half cover or fully cover the curtain roll.
Ideally if you always order the roller door with a full hood cover then you have the curtain roll neatly coiled up inside the hood cover and you would also benefit a little from some extra protection, not only for the curtain, but also in terms of air ingress. Some manufacturers only offer the roller door with a full hood as standard, Hormann and Garador are one example, along with our own Premium ROLL77 roller doors.
All the aluminium roller garage doors we offer online will have the option or it will be standard and included in the prices.
A full hood cover will assist in the best possible protection and insulation from bad weather and dust and wind ingress.
General Guidance
Internal Face Fitting
If you are installing your roller door to the inside face of your garage opening with sufficient headroom you can order the roller door with the No Hood option and you wil see the fully exposed curtain when the door is open and the barrel when the door is closed.
Inbetween Fitting
If you are installing the door inbetween your structural opening and you are also installing underneath the lintel then you will see the curtain from the outside and ideally need the Half Hood cover option to provide a fascia at the front outside, or the Full Hood Cover to enclose the whole roll inside and out.
External Fitting
If you are installing the roller door outside the opening on the outside face then you definitely need the Full Hood cover to cover the curtain from the outside view and protect from the elements.
A full hood is also preferable if your roller door isn't very high to avoid potential entrapment when the roller door is opening regardless of position. A full hood is preferable in most cases simply to protect the curtain and keep everything neatly covered.