With UK energy prices still higher than many households would like, keeping your home warm without overspending is a real challenge.
One of the biggest sources of heat loss is through old (15+ years) or inefficient windows. Upgrading to energy-efficient glazing can dramatically reduce your bills and improve comfort—without compromising on natural light.
Even if you already have double glazing in your home, if your windows are more than 10–15 years old, upgrading to Pilkington UK’s latest energy efficient glass could significantly cut your energy bills*.
Two of the best options available today are Pilkington K Glass™ S and Pilkington Optitherm™ S1 Plus. Here’s how they work, and why they could make a big difference in your home this winter.
What Is Pilkington K Glass™ S and How Does It Save You Money?
Pilkington K Glass™ S is our most popular type of low-emissivity (low-E) glass, designed to reflect heat back into your home while letting in free heat from the sun (known as passive solar gain).
When used in double glazing, it:
- Has a very neutral appearance with a high light transmittance
- Reduces reliance on central heating
- Keeps rooms warmer for longer
- Significantly reduces heat loss compared to older glazing
- Reduces the risk of internal condensation
This makes it a cost-effective upgrade for homeowners looking to improve comfort and save on energy bills.
Why Choose Pilkington Optitherm™ S1 Plus for Maximum Efficiency?
If you want even greater performance, Pilkington Optitherm™ S1 Plus is the next step up.
- Achieves a centre pane U-value of 1.0 W/m²K in a double-glazed unit
- Achieves a centre pane U-value as low as 0.5 W/m²K in a triple-glazed unit
- Ideal for areas where excessive heat loss is a concern, such as conservatories , glass extensions, and north-facing rooms where heat loss is more noticeable
- Helps maintain a consistent indoor temperature—even in colder UK climates
Upgrading PVC-U Double Glazing that is 15+ years old to high performance double glazing with Pilkington Optitherm™ S1 Plus can improve window energy efficiency by up to 230%*.
Simply put, it’s the ideal choice if you’re investing in a new build or upgrading areas of your home that lose heat quickly.
Real Savings and Everyday Comfort
Modern energy-efficient glass is up to 5x better at reducing heat loss than windows installed just a few decades ago.
By upgrading to modern energy-efficient glass, UK households can benefit from:
- Lower heating bills – saving hundreds of pounds over the lifetime of your windows
- Improved EPC ratings – making your home more attractive to future buyers
- Greater comfort – no more draughts, cold spots, or condensation on the inside of glass
For example, in a typical semi-detached UK home with single glazing, upgrading to efficient double glazing can cut carbon emissions by up to 0.83 tonnes per year. That’s good for your wallet—and the environment.
Perfect for Both Retrofits and New Builds
Whether you’re replacing ageing windows or building a new home, Pilkington K Glass™ S and Pilkington Optitherm™ S1 Plus are designed to fit seamlessly with modern window frames.
Both Pilkington K Glass™ S and Pilkington Optitherm™ S1 Plus can help windows and doors to meet current Building Regulations Part L requirements, ensuring your home complies with the latest UK energy efficiency standards.
Long-Term Value for Your Home
Energy-efficient glazing is more than just a short-term fix for high heating bills:
- It reduces household running costs year after year
- Supports sustainability goals by lowering energy use
- Could increase the value of your home by 14-38%***
Ready to Upgrade?
Don’t let another winter’s worth of energy go to waste. Upgrading your windows with Pilkington K Glass™ S or Pilkington Optitherm™ S1 Plus can help you stay warm, save money, and shrink your carbon footprint.
Ask your local window fitter for Pilkington K Glass™ S or Pilkington Optitherm™ S1 Plus today and start saving.
For more detailed information about these products, you can download our brochures here:
Pilkington K Glass™ Range brochure
Pilkington Optitherm™ S1 Plus brochure
* Figures taken from GGF’s Infographic ‘Generations Windows v 1.0’
** Calculated using the GGF Energy Savings Calculator (https://www.ggf.org.uk/myglazing/environmental-hub/energy-calculator/)
***Figures taken from UK Government’s Press Release ‘Energy saving measures boost house prices’ (https://www.gov.uk/government/news/energy-saving-measures-boost-house-prices)