Vacuum glass vs HR++ glass: which is better for your home?

Do you want to replace old glass and are you unsure between vacuum glass and HR++ glass? Then you probably look at insulation, price, thickness and whether the glass fits in your existing frame. Both types of glass are good choices, but they are not intended for the same situation. The short rule: choose HR++ glass if you have enough space in your frame and are looking for good value for money, and choose vacuum glass if you have little space, want to keep old frames or want maximum insulation without thick glass.

In this article we compare vacuum glass and HR++ glass on insulation, thickness, price, comfort, noise, subsidy and applicability, so that you can proceed with a clear selection aid.

What is HR++ glass?

HR++ glass is insulating glass with two glass plates and an insulating cavity between them. That cavity usually contains noble gas, such as argon. In addition, one of the glass plates has a special coating that reflects heat back inside.

HR++ glass is often used to replace:

single glazing
old double glazing
leaky double glazing
outdated insulating glass

It is popular because it insulates well, is affordable and often fits into existing window frames. You can customize your HR++ double glazing with the structure that suits your frame.

What is vacuum glass?

Vacuum glass also consists of two panes of glass, but the space between them is extremely thin and vacuumed. Because there is almost no air between the glass plates, heat is much less easily transmitted. The big advantage: vacuum glass insulates very well while it is much thinner than HR++ glass or triple glass.

Vacuum glass is often chosen for:

old wooden frames
monumental window frames
narrow rebates
renovations
homes where thick insulating glass does not fit
projects where the existing appearance must be retained

Image: Cross-section of vacuum glass showing the thin vacuum space and micro spacers between both glass plates

The main difference

The biggest difference between HR++ glass and vacuum glass is the construction. HR++ glass uses a relatively wide cavity with gas filling. Vacuum glass actually uses a very thin vacuum space.

Attribute	HR++ glass	Vacuum glass
Construction	Two glass plates with gas-filled cavity Two glass plates with thin vacuum space
Thickness	Often 24–28 mm	Often 8–12 mm
Insulation	Good	Very good
Price	Lower	Higher
Fits in old window frames	Sometimes	Often
Best Application	Standard renovation	Narrow or monumental window frames

Bottom line: HR++ glass is often the practical and affordable choice, while vacuum glass is especially strong when space is limited.

Insulation value: which glass insulates better?

Vacuum glass usually insulates better than HR++ glass. This is because the vacuum space greatly limits heat transfer. The insulation is expressed in the U-value: the lower, the better.

Type of glass	Insulation
Single glazing	Bad
Old double glazing	Moderate
HR++ glass	Good
Vacuum glass	Very good
Triple glass	Very good

In practice, better insulation means:

less heat loss
a warmer glass surface on the inside
less cold
a more comfortable indoor climate
a lower heat demand

Vacuum glass therefore wins on pure insulation. But that doesn't automatically mean it's always the best choice. Would you like to compare the values yourself? Then use the U-value calculator.

Thickness: why is vacuum glass so interesting?

The thickness is one of the biggest advantages of vacuum glass. HR++ glass is often about 24 to 28 mm thick and triple glass is often even thicker. Vacuum glass is usually much thinner, often around 8 to 12 mm.

This makes vacuum glass interesting for existing window frames where there is little space. Especially in old homes, window frames are often made for single glazing, which means there is little rebate depth available. HR++ glass sometimes does not fit there without adjustments. With vacuum glass you can often insulate well without replacing the entire frame. You can read more about this in thicker insulating glass in an existing frame.

Does HR++ glass fit in existing window frames?

HR++ glass often fits into existing window frames, but not always. Therefore check:

rebate depth
glass thickness
space for the glazing band
space for glazing beads
kit room
condition of the frame
weight of the window

HR++ glass often fits well in frames that previously had double glazing. It can be more difficult with old window frames with single glazing. Sometimes you can work with top slats, nosing slats, adapted glazing beads or renovation profiles. That does change the appearance of the frame.

Does vacuum glass fit in existing window frames?

Vacuum glass often fits better in narrow existing window frames. That's exactly why it's popular in renovations. It is especially useful when:

HR++ glass is too thick
you want to keep existing window frames
the frame has a narrow rebate
you want to preserve the historic appearance
new window frames are undesirable or expensive
you want high insulation without a thick glass structure

However, you should also check carefully whether vacuum glass fits. The thickness is favorable, but the window must still be able to be installed correctly with sufficient support and sealing. In practice there is more to it; read vacuum glass in practice and micro spacers.

Price: what is cheaper?

HR++ glass is usually cheaper than vacuum glass, both in terms of material costs and often also for installation. Vacuum glass is technically more advanced and therefore more expensive. However, vacuum glass can be financially interesting if it allows you to keep existing window frames. So don't just compare the price per square meter of glass, but look at the total project.

Cost item	HR++ glass	Vacuum glass
Glass price	Lower	Higher
Assembly	Often standard	Can be more specialized
Frame adjustment	Sometimes necessary	Needed less often
New window frames needed	Sometimes	Less often
Total renovation costs	Often lower	Depending on situation

If HR++ glass fits without many adjustments, it is usually the most economical choice. Does HR++ only fit with major frame changes? Then vacuum glass can become more attractive.

Comfort: do you notice a difference?

Both types of glass greatly improve comfort compared to single glazing or old double glazing. You usually notice:

less cold
less draft feeling
a warmer inner window
a quieter space
less condensation on the inside
a more constant temperature

Vacuum glass can be extra comfortable because it often insulates better than HR++ glass. This difference can be noticeable, especially with large windows or windows that you sit close to. Yet HR++ glass is already a huge improvement for many homes.

Condensation: which glass helps better?

Both HR++ glass and vacuum glass can reduce condensation on the inside. The inner glass plate remains warmer, so moisture precipitates less quickly. But no glass completely solves poor ventilation.

Condensation on the inside often occurs due to:

high humidity
too little ventilation
cooking
shower
laundry drying
insufficient heating

Condensation on the outside can occur more often with well-insulating glass. That's usually not a problem; it often means that the heat stays inside. Condensation between the glass plates is a problem: the window is leaking and must be replaced. Read more about this in condensation on windows: inside, outside or between the glass and recognizing and replacing a leaking double glazing.

Sound insulation: HR++ or vacuum glass?

Sound insulation does not only depend on the type of glass. The glass structure is at least as important. Factors that dampen sound:

different glass thicknesses
laminated glass
special sound foil
the cavity structure
gap sealing
frame quality
ventilation grilles

HR++ glass can reduce noise well if the right construction is chosen. Vacuum glass can also help, but is not automatically the best choice for sound. Do you especially want less traffic noise? Then ask specifically about soundproof glass. The thermal insulation value does not say everything about sound insulation.

Appearance: do you see a difference?

HR++ glass looks like normal double glazing to most people. The cavity is visible at the edge, especially if you look closely. Vacuum glass is thinner and therefore often fits better with old window frames.

However, with some types of vacuum glass, small spacers may be visible: very small dots that keep the glass plates apart. These dots are usually not noticeable, but you can see them in certain lighting. In monumental or characteristic homes, vacuum glass can be interesting in terms of appearance, especially because the existing frame can be retained.

Weight: which glass is heavier?

HR++ glass and vacuum glass differ in weight, depending on the construction. Because HR++ glass often has a wider cavity, it is not necessarily extremely heavy; the weight is mainly determined by the thickness of the glass plates themselves. Triple glass is clearly heavier than both.

With existing rotating windows you should always pay attention to:

hinges
locks
frame weight
condition of the wood
chance of subsidence

Vacuum glass can be useful for existing windows because it is thin, but here too the frame must be suitable.

Subsidy: do you receive a subsidy for HR++ or vacuum glass?

HR++ glass and vacuum glass may be eligible for a subsidy if they meet the current conditions. Consider insulation value, minimum surface area and professional installation. Please note the following:

check the U-value
check the reporting code
Have the glass professionally installed
Save invoice and proof of payment
take photos of the work
Apply for a subsidy on time

Subsidy conditions may change. Therefore, always check the current rules before ordering. You can find more background at the ISDE subsidy for insulating glass.

When do you choose HR++ glass?

Choose HR++ glass if you want a good insulation improvement for a reasonable price. Particularly suitable for:

existing window frames with sufficient space
replacement of single glazing
replacement of old double glazing
leaky double glazing
standard renovations
homes where price is important
situations where no monumental requirements apply
projects where the glass thickness fits

For many homes, HR++ glass is the best price-quality choice.

When do you choose vacuum glass?

Choose vacuum glass when HR++ glass is too thick or when you want to keep existing window frames without major adjustments. Particularly suitable for:

old wooden frames
monumental buildings
narrow rebates
behoud van authentieke uitstraling
renovaties zonder nieuwe kozijnen
higher insulation requirements
situaties waar triple glas niet past
projects where maximum insulation is important

Vacuum glass is more expensive, but is often technically the best solution for limited space.

When should you not choose vacuum glass?

Vacuum glass is not always necessary. Do not choose vacuum glass if:

HR++ glass fits easily
your budget is limited
you do not have high insulation requirements
your window frames will still be replaced
triple glazing makes more sense with new window frames
the additional cost does not outweigh the benefit

In many standard renovations, HR++ glass is sufficient. Are you unsure between triple and the rest? Read triple glazing: when and when not, or put together triple glazing if you are installing new window frames.

When should you not choose HR++ glass?

HR++ glass is less suitable if:

your frame is too narrow
you want to fully preserve the original appearance
you want maximum insulation in a thin glass structure
you have monumental window frames
you don't have room for thicker glazing beads
the window frames may not be adjusted

In those cases, vacuum glass is often a better option.

Common mistakes when choosing

Only look at insulation value — the best insulation value is not always the best choice; the glass must also fit in your frame.
Forgot the rebate depth — without sufficient rebate depth, HR++ glass will not fit properly.
Reject vacuum glass because it is more expensive — if this prevents you from having new window frames, vacuum glass can still be interesting.
underestimating HR++ glass — for many homes, HR++ glass is already a major improvement.
Do not take ventilation into account — better glass makes your home more dense; ventilation remains important.
Confuse sound insulation with heat insulation — do you want less noise? Then choose a specific sound-resistant structure.

Selection aid: HR++ glass or vacuum glass?

Situation	Best choice
Existing frame with enough space	HR++ glass
Narrow old window frames	Vacuum glass
Maintain monumental appearance	Vacuum glass
Lowest price	HR++ glass
Best price-quality	HR++ glass
Maximum insulation in thin glass	Vacuum glass
New window frames	Triple glass or HR++ glass
Replace leaking double glazing	HR++ glass
Single glazing in old frame	HR++ or vacuum glass
Frame may not be adjusted	Vacuum glass

Checklist before you choose

How deep is the rebate?
What is the current glass thickness?
Is the frame in good condition?
Do you want to keep existing window frames?
Is the house monumental or characteristic?
Does HR++ glass fit without major adjustments?
Is vacuum glass necessary due to limited space?
How important is maximum insulation?
What is your budget?
Do you want to apply for a subsidy?
Is safety glass necessary?
Is ventilation properly arranged?

Not sure how to measure rabbet and glass thickness? Then follow the steps in measure glass.

Conclusion

HR++ glass and vacuum glass are both good choices, but for different situations.

Rule of thumb: HR++ glass = enough space + best price. Vacuum glass = little space or frame retention.

HR++ glass is usually the best choice if you have enough space in your frame and are looking for an affordable, reliable insulation improvement. It is ideal for standard renovations and replacing single glazing or old double glazing. Vacuum glass is especially interesting for old, narrow or monumental window frames: it is thin, insulates very well and often makes it possible to preserve existing window frames. The price is higher, but that may outweigh the costs of new window frames or major adjustments.

Are you in doubt? Then start with the rebate depth and the condition of the frame. Does HR++ glass fit well? Then that is often the most practical choice. Does HR++ not fit, or do you want to keep the original frames? Then vacuum glass is probably the better solution.