1. What an interior covering can change in winter

Window coverings are often regarded as providing privacy and solar shading. In winter, certain interior systems can also affect heat transfer between the room and the glazing. The material alone is not decisive: the covering, enclosed air, cavity geometry, perimeter gaps and installation distance together form the effective heat-transfer path.

The scientific literature investigates widely differing systems – fabric cellular shades, simple roller blinds, horizontal blinds and other configurations. Their results cannot readily be transferred to a movable stack of metallised films. This overview therefore consistently distinguishes component measurements, test-room experiments and building simulations.

2. Cellular shades: why air cavities and geometry matter

Cellular shades have hollow fabric cells that create additional air layers in front of the glazing. Under suitable boundary conditions, the enclosed air reduces heat transfer. At the same time, convection within the cells and airflows around the perimeter can reduce their effectiveness. Cell shape, dimensions and mounting arrangements are therefore more than aesthetic details.

In 2018, Hart investigated the thermal transmittance of windows with cellular shades through measurements, computational fluid dynamics and the WINDOW/THERM software. The study validated heat-transfer correlations, not the heating-energy savings of an entire house [1].

Hart also identified the distance between the covering and glass, the extent to which the honeycomb cells are stretched, perimeter gaps and mounting hardware as relevant factors. In particular, the large percentage model discrepancies must not be presented as correspondingly large energy savings.

3. Kunwar, Bhandari and Curcija: measurements and national simulations

Kunwar, Bhandari and Curcija compared five cellular shades – three single-cell variants and two double-cell or nested-cell variants – with conventional horizontal blinds. The experimental investigation used two nearly identical rooms in a residential house and data from two heating seasons [2].

The experiment reported daily heating-energy savings of 17 to 36 % relative to the reference case without a covering. The cellular shades were opened during the day and closed at night; night-time hours were selected for the heating-energy analysis so that differences in solar gains would not distort the result. These percentages apply to the rooms, experimental conditions and heating-energy analysis investigated; they are neither general whole-building savings nor a tested performance value for FVS.

The authors also used the measurement data for energy simulations of a residential building prototype. In cold climate zones, the modelled savings reached up to 9 kWh per m² of conditioned floor area per year. For the heating and cooling components of site energy demand considered, modelled savings of up to approximately 9 % with a heat pump and approximately 15 % with gas heating were reported, in each case relative to cases without window coverings. These figures come from simulations and must not be interpreted as measured reductions in national energy consumption.

4. PNNL Lab Homes: a controlled comparison of buildings

At Richland, Washington, the Pacific Northwest National Laboratory investigated two matched, all-electric Lab Homes, each with around 1,500 square feet (approximately 139 m²) of living space. In the experimental home, Hunter Douglas Duette Architella Trielle cellular shades were installed over existing double-glazed windows with aluminium frames; depending on the experiment, the baseline home had either no covering or conventional white horizontal blinds [3].

The report covers winter heating operation in 2015/2016 and summer cooling operation. The Hunter Douglas Duette Architella Trielle system investigated consisted of six fabric layers, including two opaque layers, and five insulating air cavities. The air cavities were lined with a layer of metallised Mylar to reduce, among other things, radiative heat exchange. Despite this shared feature of reflective multilayer principles, the fabric honeycomb geometry must not be equated with a movable stack of metallised films. Since operating schedules, the reference case and the relevant loads are crucial to percentage figures, no single PNNL energy-saving percentage is reproduced here without a complete identification of its experimental phase and reference quantity.

5. Chhetri and Zhong: position and spacing of an interior roller blind

In 2025, Chhetri and Zhong investigated an interior roller blind in a cold climate zone using in-situ measurements and numerical simulation. They compared fully open, fully closed and half-open positions [4].

Relative to the open reference case, the study reports a reduction in energy losses within the assessed balance of 11.25 % with the blind closed and 5.34 % with it half open. These values characterise the heat or heating-energy balance evaluated for the office and period investigated; they must not be interpreted as a general reduction in total building energy consumption. In its highlights, the publication describes the closed case as ‘heating energy savings over 4 months’, whereas the abstract uses ‘energy loss’. Without a detailed reproduction of the assessment boundary, these values are deliberately not reinterpreted here as a universal reduction in delivered energy.

The numerical investigation also showed that thermal transmittance depends on the distance between the blind and glazing: in the modelled configurations, the U-value initially decreased as this distance increased, then approached a limiting range. This does not establish a universally optimal spacing for all blinds, window sizes and temperature differences.

6. Comfort: a related but separate question

Interior coverings can change not only heat flow but also the local radiant environment. Frontini and Kuhn investigated how the longwave surface properties of interior blinds need to be accounted for when calculating mean radiant temperature. Their frequently cited value of approximately 1 K concerns a specific summer model configuration near the façade; it is not a general winter comfort improvement [5].

The more detailed publication ‘Radiant Comfort in Front of the Window – What Scientific Studies Show and What This Means for Dynamic Thermal Protection’ addresses the particular influence of low-emissivity surfaces, measurement methods and the testing still required on the present-day FVS.

7. Conclusions that can be drawn across the studies

The studies agree that an interior system cannot be described by fabric thickness alone. However, a fabric cellular structure and a metallised film stack differ in surface radiation, airtightness, mechanics, cavity geometry and material behaviour. Each requires its own measurements.

8. Relevance to the development of dynamic multilayer film-based thermal protection systems

Research on cellular shades and roller blinds establishes several physical and construction principles that are also relevant to the development of multilayer interior thermal protection systems. It does not, however, validate the thermal performance of the present-day movable FVS. A robust comparison requires defined material properties, cavity spacings, perimeter sealing, movement and actual installation conditions, together with measurements of the complete system.

An additional distinguishing feature of movable systems is their operating strategy: when closed, a covering can reduce heat loss; when open, it can admit solar gains and daylight. Whether this is beneficial over a heating season can only be assessed over time and within a consistent system boundary.

9. Conclusion

Interior window coverings can provide a technically significant additional thermal resistance in winter. Experiments demonstrate lower heat losses or lower heating-energy use under defined conditions. However, the magnitude of the effect depends on geometry, spacing, perimeter gaps, installation, operating strategy and the assessment boundary. The results provide a research basis for development, rather than direct evidence of product performance for movable metallised film systems.