NZ Case Study: Retrofitting Double Glazing versus 3M Thinsulate Installation

Compare the costs and benefits of 3M Thinsulate versus Double Glazing in NZ – South

NZ Case Study:  Retrofitting Double Glazing versus 3M Thinsulate Installation

Retrofitting Double Glazing versus 3M Thinsulate Installation: Cost Comparison for New Zealand, South Island.

[Article Updated August 2019]

Complete Film Solutions is excited to announce expansion plans into the South Island of New Zealand, with the aim of bringing 3M Thinsulate Window Film into the perfect market for this product.  The areas of South Canterbury, Otago and Queenstown suffer through some bitterly cold winter weather (we swear that wind comes directly up from Antarctica), yet are experiencing warmer Summers every year (thank you climate change!)

Many of our friends and family in the land of the long white cloud are trying to save money to retrofit double glazing for their homes to improve their year-round comfort levels and reduce their energy bills.

In this article, we will explain the pros and cons of retrofitting double glazed units (i.e. removal of your entire window of single pane glass, including the frame structure and replacement with a brand new double glazed unit), and compare these against the pros and cons of installing 3M Thinsulate Window Film – a revolutionary new product from 3M that is manufactured using the latest technology to prevent heat loss through your glass in winter, and reject heat from the sun in summer.

Before we get into the pros and cons, and our case studies, let’s spend some time understanding the terminology used when talking about energy efficient glass options.

What is Double Glazing?

Double glazing (also known as DGU or IGU) consists of a fully sealed unit, with 2 panes of glass separated by a space.  The space is filled with air (for cheaper, lower performing double glazing), or in higher specification double glazing, the space is filled with the higher performing Argon gas, which is a better insulator than air.

Double glazing can vary widely, depending on glass thickness, width of the air/ gas space, use of different glass types (for example, toughened glass, laminated glass, low-e glass, tinted glass).  All these variables contribute to high variation in the cost of double glazing.   They also mean that there is a wide variance in the performance ratings of double-glazed units.

The cheapest form of double glazing is one where an additional frame and glass is just added to your existing window, sometimes via the use of magnets or other means of attachment.  As this form of double glazing cannot guarantee an air-tight seal, these types of double glazing will only have an air-filled space.  The higher performing argon units have the argon gas installed in the factory when the glass is completely sealed to be air-tight.

Lower performing double glazed units will also have aluminium frames.  Aluminium is known to be a very poor insulator.  High performance double glazing will usually have timber or PVC frames, both of which are better thermal insulators than aluminium.

What is Low E Glass?

Low-E Glass is short hand for “low emissivity”.  Low E glass is designed to release less heat energy.  Normal glass releases high levels of heat into the space around the glass – this heat release is transformed into undesirable heat loss during cooler seasons, and unwanted additional heat gain in summer.  Low E glass is created when a low-e coating is fused onto one side of the glass during the manufacturing process.  Any type of glass can be made into low-e, including double glazed units. With the building code requiring attainment of a minimum level of energy efficiency, it is unlikely that single glazed low-e glass is common in New Zealand, but it is an upgrade option in double glazed units to get even higher performance.

What is 3M Thinsulate?

3M Thinsulate is a low e window film that is applied to the internal surface of existing glass.  It is an ideal, cost effective and high-performance alternative to retrofitting of double glazing to older homes.  Manufactured by 3M in the USA, Thinsulate has a neutral appearance that will not dramatically change the look of your windows.  It will also block 99% of UV rays, which is the leading cause of fading of furniture, flooring and window treatments.   During Winter, it will help keep the warmth in, and will still allow passive heat from the sun to enter your home – the difference is that with Thinsulate on your windows, that passive heating isn’t immediately being lost straight back through your glass!  During Summer, it will keep the heat out, and help retain any cool air inside your home.    Use of Thinsulate will even out hot and cold spots in your home, improve overall comfort levels and allow you to keep your curtains open during winter, to allow the sun to come in, without feeling the cold air standing next to the window.

What values do you need to compare when looking at energy efficient glass options?

There are two main values to look for when comparing the technical details of energy efficient glass options.  U value is a measure for the cooler months, as it refers to the thermal performance of a material – i.e. how well it insulates against cold.  The lower the U-value, the better it performs as an insulator in both summer and winter.

Solar heat gain coefficient (or SHGC) is the measure between 0 and 1 for performance comparison during the warmer months – as it measures how much heat is gained through your windows from the sun.  The lower the number, the better the material performs at rejecting heat.

Compare the performance of double glazing and 3M Thinsulate in the table below (Sources – Viridian Glass Specification and 3M Thinsulate Specification documents):

Glazing TypeU Value (w/m2 K) lower = betterSHGC (G Value) lower = betterUV Light Transmission

lower = better

Cost Comparison
Baseline – standard 6mm clear single glazing5.80.8260%
3M Thinsulate Climate Control 40% (Tinted) on 6mm clear glass3.60.41< 0.2%$
3M Thinsulate Climate Control 75% (Clear) on 6mm clear glass3.60.53<0.1%$
DGU 4mm clear, 12mm gap, 4mm clear, air filled (Refer Case Study #3)2.70.7551%$$$
DGU 6 mm clear, 12 mm gap, 6mm clear, air filled2.70.7144%$$$$
DGU 6mm clear, 12 mm gap, 6mm clear, argon filled2.50.7144%$$$$
DGU 6mm clear, low e coating on Surface #2, 12mm argon-filled gap, 6mm clear (Refer case Study #2, for opening windows only, all others were add on hardware/ glass)1.70.5623%$$$$$$$



Advantages of New Double-Glazed Units

The positives of retrofitting existing windows with new double-glazed units include:

  • Reduction of neighbourhood, traffic or other external noise
  • Reduced heat loss through the glass in winter
  • Reduced heat transmission through the glass in summer
  • Improved energy efficiency
  • Reduce or remove condensation build up on glass in cold weather
  • Updated and improved aesthetics from brand new window frames and glass installed
  • Usually a 5-10-year warranty

Disadvantages of New Double-Glazed Units

The drawbacks of retrofitting existing windows with new double-glazed units include:

  • High cost – see our case studies below for more detail
  • Where the lower cost option is chosen to retrofit by adding additional glass and framework to create a 2nd layer of glass to existing windows, this adds additional bulk, and may not look as aesthetically pleasing when adding to existing frames. It also not as high performing as a full DGU replacement, as the glass cannot guarantee a perfectly sealed unit.
  • Disruption to the home owner by removal and replacement of windows
  • Dirt and dust created from installation process
  • Potential damage to the home from removal of existing windows/ install of new windows
  • Very high replacement cost should a DGU be broken or damaged

Advantages of 3M Thinsulate

The positives of installing 3M Thinsulate low-e insulating window film to existing glass include:

  • Considerably more cost and time effective to install than double glazing or installation of low e glass.
  • Achieves similar benefits to double glazing in heat retention during winter.
  • 3M Thinsulate, in both the 40% VLT and 75% VLT (visible light transmission), achieves higher heat rejection performance than double glazing in Summer. Let’s review the Solar Heat Gain Coefficient (SHGC) for each.  Remember, SHGC is a measure of heat gain through glass from sun and is a figure between 0 and 1.  Numbers closer to 0 reflect better rejection of summer heat. Double glazed units typically record a Solar Heat Gain Coefficient of around 0.56 (low-e double, argon filled glazed unit) to 0.75 (for clear, air filled double glazing).  Thinsulate window film achieves a SHGC of between 0.41 (for 40% VLT option) and 0.53 (75% VLT variant).
  • Clean installation process that minimises disruption to the home owner, as the film is applied to your existing glass.
  • Easier installation for multilevel homes or apartments, where removal and installation of an entire window unit would be difficult and risky due to working at heights, compared to installing film from the inside on existing glass.
  • Original windows and glass are retained, so your home appearance does not change. The 75% VLT option of 3M Thinsulate is near invisible on your glass, so there will be no noticeable difference between how your windows look before and after installation.
  • Improved energy efficiency resulting in much lower energy bills for heating and cooling your home.
  • Low long-term maintenance costs – if a window fitted with Thinsulate film is damaged or broken, cost of replacing with standard glass and new film is much lower then replacement of a DGU or low e glass
  • 3M provides a Lifetime manufacturer’s warranty for Thinsulate window film when it is installed by a 3M Licensed Installer.  This is for residential homes for the original film purchaser for the lifetime that they own the home.  Commercial properties are provided with a 15 year warranty.

Disadvantages of 3M Thinsulate Window film include:

  • Will not improve the aesthetics where existing window frames are in poor or unsightly condition
  • Is not designed to assist with noise reduction
  • Compared to double glazing, a little extra care is needed in cleaning windows with Thinsulate applied to prevent scratches in the film – this is not onerous and will only require minor changes to how you might normally clean your windows
  • For best results, 3M Thinsulate will perform better in homes where condensation build up on windows is minimal or controlled (through use of extraction fans in bathrooms and kitchens, regular airing of your home and/or installation of a home ventilation system). If your home suffers from excessive damp or condensation build-up, then 3M Thinsulate will not work as effectively to reduce heat loss in winter.

Case Study 1

Let’s compare the cost of retrofitting double glazing with 3M Thinsulate film install.

Claire obtained a quote for retrofitting double glazing to 4 window sets in her home, just south of Timaru, New Zealand.  The rooms being quoted were the main bedroom (5 panel window); Dining Room (5 panel window); Living Room (5 panel window) and a Bay Window (5 panel window).  This quote was a retrofit solution, installing new glass and additional framing within existing framing for fixed windows, while doing a full removal and replacement of windows and framing for opening windows.

The quote received was as follows:

CompanyDetails / InclusionsTotal Project Price (including GST)
AClear toughened glass, bronze anodised 12M frames, air filled, total 14.1 sqm.$7,240.08


Next, the same measurements for all 20 panels were used to calculate a quote for supply and installation of 3M Thinsulate low-e insulating window film.

The final quote came to: $4,403.93 including GST.  This is 39.2% cheaper than retrofitting double glazing.

Case Study 2

Andrew and Kay obtained a quote for retrofitting double glazing to their Kitchen, Dining and Lounge Rooms – 21 panels of glass in total for their home in Timaru.  The quote received was a retrofit solution, where additional framing and new glass was installed within existing frames for all fixed panels (11 panels in total).  All opening windows (10 of the panels overall) would be a full remove and replace of both glass and framing with a new double-glazed unit.   The quote received was as follows:

CompanyDetails / InclusionsTotal Project Price (including GST)
BClear Glass – addition to existing fixed panels x 11 panels, Grey tint glass/ clear glass double glazed units x 10 for replacement of existing opening panels, with low-e glass and argon gas upgrade.$9,845.00


Next, the same measurements for all 21 panels were used to calculate a quote for supply and installation of 3M Thinsulate low-e insulating window film.

The final quote came to: $4,411.86 including GST.  This is 55.2% cheaper than retrofitting double glazing.

Case Study 3

Damien and Sally obtained a quote for retrofitting double glazing to their whole home – 9 window/ door sets (consisting of 17 Double Glazed units, or 24 individual windows of glass) in total for their home in Temuka.  The quote received was a full remove and replace of existing windows with all new double-glazed units (so this is a more extensive option than those presented in Case Studies 1 and 2).  The quote received was as follows:

CompanyDetails / InclusionsTotal Project Price (including GST)
CPowder Coated Aluminium Framed Double-Glazed Clear windows (Obscure glass to amenities), 4mm clear glass, air gap, 4-5mm glass – combination of toughened or float.$29,053.07


Next, the same measurements for all 24 panels of glass were used to calculate a quote for supply and installation of 3M Thinsulate low-e insulating window film.

The final quote came to: $8858.11 including GST.  This is less than ONE THIRD of the cost of a full double glazing installation.


Outcome: 3m Thinsulate Most Cost-Effective Solution

3m Thinsulate is the clear winner, in terms of benefits and cost effectiveness. Before making the decision on whether to go for retrofitting double glazing or installing 3M Thinsulate window film, consider the following:

Benefits of 3M Thinsulate Window Film
1.       3M Thinsulate Window Film is 39-55% cheaper than the cost of retrofitting double glazing, where only partial replacement occurs, but majority of double glazing is just additional glass and hardware to your existing frames.
2.       3M Thinsulate is less than ONE THIRD of the cost of a full Double Glazing installation, where the entire existing window frame is removed and replaced with a fully sealed, brand new double glazed unit.
3.       A LIFETIME warranty for 3M Thinsulate versus only 5-10 year warranty for double glazing
4.       3M Thinsulate Performs Similarly to Double Glazing for Winter Heat Retention and OUTPERFORMS Double Glazing for Summer Heat Rejection – an important consideration as New Zealand’s Summers continue to heat up.


Complete Film Solutions are 3m Licensed Installers. Contact our expert team today to discuss your requirements and the benefits of installing 3M Thinsulate in your home.



Get in early to see us at the Timaru Home Show from 13 to 15 September 2019.  The first 5 confirmed installation bookings from the show will receive a 25% discount from the RRP.  All other Home Show visitors will receive a 10% discount.

**Update – Testimonial

Remember Andrew and Kate from our case study? They stood to save more than 55% of the quoted cost for retrofitted double glazing by installing 3M Thinsulate instead.
On 16th May 2019, Andrew and Kate were our first completed install in New Zealand, and they are delighted with the results! Here are Kate’s words:
“We would like to say a very big thank you to CFS for their advice and expert installation of 3M “Thinsulate” window film.
We wanted to reduce our heating costs, but after getting quotes for double glazing, we decided that we could not justify the cost.
We later read about a Thermal Window Film and researched this product. Acting on advice from Brent, the owner and installer, we took the plunge and had Thinsulate Window Film applied to all windows and doors in our living area today and the results are unbelievable. It is like Summer all year long!
Once again, our grateful thanks, Andrew and Kate”

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