The wearing of an LBV or QRV should always be done as close to the skin as possible by means of the combat shirt whether or not with additional under layers such as a T-shirt e.g.
It is important that none of these layers should create pressure points between the ballistic protection and the layers you wear underneath.
This is not only to increase comfort, but will also protect you better. Pressure points, created by buttons and zips, can cause additional injuries in case of and reduce the effectiveness of the ballistic protection by not fitting closely enough to the shape of your chest and/or back.

The High Loft Jacket features a camouflage pattern and can therefore be worn as an outer layer both in and out of the quarter.
The High Loft Jacket has very good thermal values and primarily serves to retain body heat during downtime or low activity. In moderate and high activity, your body heat will increase, and the High Loft Jacket will not allow you to regulate (read cool down) your body heat.
The High Loft Jacket is water-repellent, meaning it can withstand light precipitation for a short period of time. If normal to heavy precipitation falls over a longer period, it is recommended to wear rainwear (possibly over the High Loft Jacket).
The above is highlighted below with specific cases (this list is non-exhaustive, in case of doubt you can always contact the equipment manager).

HIGH LOFT JACKET

Active = Person performs certain (operational) activities in an active/moving state:

I am running the course on the obstacle course, can I wear my High Loft Jacket? NO
I am hiking (marching) with my backpack, can I wear my High Loft Jacket? YES (However, underlayers are provided that can provide extra warmth, this often makes it unnecessary to wear the High Loft Jacket during this activity).
I am walking with or without a backpack, can I wear my High Loft Jacket? YES (However, underlayers are provided that can provide extra warmth, this often makes it unnecessary to wear the High Loft Jacket during this activity).
I am (dynamically) performing an infiltration with backpack, can I wear my High Loft Jacket? NO
I am dynamically performing an infiltration with QRV/LBV, can I wear my High Loft Jacket? NO
I am conducting a patrol with my QRV/LBV, can I wear my High Loft Jacket? NO (Underlays are provided to provide additional warmth).
I am climbing a mountain, can I wear my High Loft Jacket? NO
I perform a dynamic tactical activity, can I wear my High Loft Jacket? NO
I perform a dynamic tactical activity specifically in a wooded area, can I wear my High Loft Jacket? NO
I am providing assistance to the nation in active operations e.g.: debris clearance after a natural disaster (flooding), can I wear my High Loft Jacket? NO
I am performing a jump, can I wear my High Loft Jacket? NO
I am performing a parachute jump without QRV/LBV, can I wear my High Loft Jacket? YES
I perform a Fast Rope with QRV/LBV, can I wear my High Loft Jacket? NO

Semi-Static = Stationary person performs moving activities:

I am semi-static firing (upright or lying down) with my QRV/LBV on, can I wear my High Loft Jacket under my QRV/LBV? NO (It is not permitted to wear the high loft jacket under the QRV / LBV. Underlayers are provided to provide extra warmth).
I am semi-static firing (standing or lying down) without QRV/LBV on (but e.g. only with belt and holster), can I wear my High Loft Jacket? YES
I am in a vehicle without QRV/LBV and ascending and descending, can I wear my High Loft Jacket? YES
I am driving an open or closed vehicle with my QRV/LBV on, can I wear my High Loft Jacket? NO
I am driving an open or closed vehicle without my QRV/LBV on, can I wear my High Loft Jacket? NO
I am providing assistance to the nation in static operations e.g.: offering food (packages) after a natural disaster, can I wear my High Loft Jacket? YES
I am a mechanic and perform repair or maintenance work on a vehicle, aircraft..., can I wear my High Loft Jacket? YES, under the overall or PPE jacket provided
I am performing a ceremonial ceremony (possibly with weapon), can I wear my High Loft Jacket? NO (Medals are not allowed on the high loft jacket).
I perform a (the weekly) flag salute in my unit (possibly with weapon), can I wear my High Loft Jacket? YES
I perform manipulations with weapon in dry training (TGS), can I wear my High Loft Jacket? YES

Static = Person is in stationary position:

I take a short break after walking/running, can I wear my High Loft Jacket? YES (RECOMMENDED)
I am stationary at the shooting range in the standby zone where I am refilling ammunition in my loader SCAR in cold, dry weather, can I wear my High Loft Jacket over my QRV/LBV? YES
I am on watch, can I wear my High Loft Jacket under my QRV/LBV? NO (It is not allowed to wear the high loft jacket under the QRV/ LBV. Underlayers are provided to provide extra warmth).
I am on watch (without QRV or LBV), can I wear my High Loft Jacket as an outer layer? YES

FIELD SHIRT
The field shirt can be worn in all (above) conditions.
However, it is not allowed to wear it under QRV/LBV.
The BDCS System is a multi-layer system. The field shirt does not provide insulation by itself, but can be combined with various underlayers and the High Loft Jacket.
The field shirt replaces the 'old' field shirt and combat vest.

How do I wear an LBV or QRV in combination with BDCS clothing ?