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Home & garden.

Updated: 3 May 2022

Which is the best type of double glazing?

Find out all you need to know to choose the best type of double-glazed windows and doors for your home, as well as the right material, from uPVC, timber and aluminium.
Sarah Ingrams
Double glazed glass in a window frame 453535

With such a dizzying array of different types of windows and doors, as well as materials and finishes, it can be hard to know which ones to choose.

From sash to bay windows, and sliding to French doors, we explain the key differences between them to help you choose what's best for your home. Click on the links below to head to the section you want.

Once you've flicked through our galleries, we'd recommend asking a few double glazing companies to come to your home to give you advice, explain the types of products they have available, and to get an idea of cost.

Visit our double glazing reviews to discover which national company was rated highest and lowest.

What type of double glazed windows are right for my home?

Our gallery shows the various types of double-glazed windows and materials. Scroll down below to see more information about each.

Double glazed window types

A large collection of images displayed on this page are available at https://www.which.co.uk/reviews/double-glazing/article/how-to-buy-double-glazing/choosing-double-glazed-windows-and-doors-auxkN5y2Y0Zn

The images of double-glazed windows and doors above are from Anglian, Everest and Safestyle. See how each company was rated by its customers by visiting our double glazing reviews.

Double glazed casement windows

Casement windows are attached to the frame with one or more hinges, typically allowing them to open to the side. They can instead be hinged at the top or bottom, making them 'tilt and turn' windows – you can find out more about these types of windows below.

They usually open inwards, which generally makes them easier for cleaning. They are held open by 'casement stays' – small metal bars that open and close in a scissor motion. 

Casement windows are often uPVC, but can also be made of timber and aluminum – read on below for more details about window materials. Many companies also offer different colour options.

Flush casement windows (as in the picture above) are similar but sit close to the frame, so they're in line with it, rather than proud.

Double glazed sash windows

Sash windows typically open by lifting a pane and its frame up or down. You can either have:

  • single-hung windows – where just one pane moves, typically the bottom, while the other is static
  • double-hung windows – this means both panes can be moved, one up and the other down.

You can also get tilt-and-turn versions. Like with casement windows, they come in a range of different materials and finishes.

They're a great way to add a traditional or authentic feel to a period property. Old sash windows are known for not being particularly energy-efficient. But modern designs employ the same double glazing technology as other windows. 

Bay windows

Bay windows protrude from a house, either sitting in a curved bay that gives some extra floor space, or as a protruding window bay with a deep sill.

They usually house three or more windows, and you can have any type, material or finish. As well as being a great design feature, they add extra space to a home. The two side windows allow more light in and enable you to have panoramic views.

Tilt and turn windows

Casement windows can also come with a tilt-and-turn hinge, which means they can be tilted open. Different designs allow you to open the windows to varying degrees. They typically open slightly, so that they can be left ajar, but some can tilt up to 90 degrees.

Some come with notched catches to hold them open at different points, as in the image below. As they can be locked partially open, they're a secure way to allow some fresh air into your home. That said, some non-tilt and turn windows can also be locked in an almost closed position for security. 

You can also get dual-turn windows, where two windows sit one on top of the other and both tilt open. Some double glazed doors come with the ability to tilt, too.

UPVC double glazed windows

The most common type of window frame for double-glazed windows is uPVC (unplasticised polyvinyl chloride, to give it its full name). Not only is it up to three times cheaper than traditional wooden frames, but it's also recyclable, durable and the most energy-efficient type of frame.

uPVC window and door frames are available in a variety of colours and finishes, including wood, though they're most commonly white. uPVC is easy to keep clean, too, requiring little more than a wipe down with a soft cloth and a spot of washing-up liquid every now and again.

Wooden/timber windows

Timber is a greener material than uPVC, as it's naturally renewable. Many people feel wooden windows look nicer and more subtle than uPVC, particularly in traditional or period-style properties.

While timber windows tend to be more expensive and need maintenance, they can last a very long time if properly looked after.

Aluminium double glazed windows

Aluminium is a very strong material, so its windows are durable and low maintenance. It's also slimmer and lighter than other materials, so can give a sleek, modern look.

Although you'd assume aluminium windows are grey or metal in colour, many manufacturers offer lots of different options.

You can find out more about the cost of different types of windows and materials by visiting our page on double glazing prices. Once you're ready to start shopping, our page on double glazing quotes and sales tactics will help you avoid common sales tricks. 

What type of double glazed doors should I choose?

Double-glazed doors are a great way to bring the outside into your home, as well as let in light. Our gallery shows the various types of double-glazed doors. Scroll down below to see more information about each.

Double glazed door types

A large collection of images displayed on this page are available at https://www.which.co.uk/reviews/double-glazing/article/how-to-buy-double-glazing/choosing-double-glazed-windows-and-doors-auxkN5y2Y0Zn

Patio sliding doors

Patio sliding doors, often referred to as just patio doors or sliding doors, are glass doors that slide open. Typically one moves while the other stays static, but you can have both sliding. 

They're a good space saver, as they won't encroach on your garden or home. Sliding doors can be uPVC or aluminium, and come in a range of colours and finishes.

Double glazed French doors

Sometimes called ‘French windows’, these glass doors open out like casement windows. Although both can open, you can choose to have one open at a time and keep the other closed.

As well as aluminium and uPVC, French doors can come in wood, too. Again, there are lots of finishes available.

You might want to use 'stays' – hooks to ensure the door stays open and doesn't fly back or slam shut in the wind.

Bi-fold doors

Bi-fold doors are a set of two or more glass doors that fold back onto each other in a concertina. With these types of doors, you won't need anything to hold them open as they automatically stay where you've opened them.

They come in aluminium and uPVC and various colours. They're a typically stylish, contemporary option, particularly if they are in aluminium. 

Should I buy triple-glazed windows?

Triple-glazed windows have a third pane of glass, so they should make your home warmer and more sound-proof than double-glazed windows. Some companies also use different types of gas between the panes to further prevent heat loss and Low-E glass to reflect sunlight inside.

As you'd expect, triple glazing is more expensive than double. If you're really keen on getting it, but the cost is prohibitive for your entire house, think about triple glazing just the rooms that get coldest or suffer worst from external noise.

You can find out what the big-name companies offer by visiting our individual pages on Anglian, Everest and Safestyle.

What is secondary glazing?

Secondary glazing involves fitting a second layer of glass inside your existing windows. It isn’t as effective as full double glazing, but it could still save you some money on your heating bills – and it's much cheaper to install.

It could also be a good alternative for homes that can't have double glazing – if you live in a listed building, for example. 

Where should I buy double glazing?

There are a couple of ways in which you can buy double glazing. You can either choose a well-known, recognised double glazing company, such as Anglian, Everest and Safestyle, or have it installed by an independent double glazing company in your local area. Some more generalist DIY stores, such as B&Q, also sell double glazing.

If you're having an extension or building a new home, you can also use the independent builder or joiner you're already coordinating with for your project. 

Find out how much you should expect to pay for double glazing to avoid being overcharged.


B&Q sells double-glazed windows and sliding patio doors in both uPVC and white-finished timber. Brands include Crystal Direct (not to be confused with Crystal Windows and Doors of Romford), Richmond and Stormsure.


You can buy double-glazed windows and skylights from Screwfix.

Windows are available in a wide range of formats and sizes, in both uPVC and white-painted timber. Brands on sale include Crystal (not to be confused with Crystal Windows and Doors of Romford) and Jeld-Wen for standard double-glazed windows, while skylight brands include Tyrem and Velux.


French patio doors are available from Wickes in several sizes and designs. All are Wickes-branded and made of uPVC.

Independent double glaziers

Some 45% of the 3,467 people we surveyed in August 2020 used an independent or local firm for their double glazing installation. Our page on independent double glaziers reveals how customers thought they compared with the bigger brands on customer service, pricing and quality.

You can visit Which? Trusted Traders to find an independent glazier near you or you can use our search tool above. All companies and traders that bear our logo have been through stringent background checks and must sign up to our code of conduct, so you can be assured they're reputable.