Best Bubble Insulation and Thermal Screen Kits

Why bubble film and not something better

There are better insulators than bubble film. There is nothing better that also lets light through, costs very little, fits a greenhouse frame without tools, and comes off again in spring. That combination is why horticultural bubble has been the standard answer for decades despite being, on paper, a mediocre insulator.

The mechanism is trapped air. Each bubble is a small pocket of still air, and still air conducts heat poorly. Two layers of film with a bubble layer between them roughly doubles the insulating value of a single sheet of glass, which sounds modest until you consider that a hobby greenhouse loses most of its heat through the glazing and that you are paying to replace every degree of it.

The trade is light. Every layer you add takes a share of the incoming light in the season when light is scarcest. That trade-off, not the insulation value, is what should drive where you fit it.

Horticultural bubble vs the stuff from the packaging shop

Packaging bubble wrap is cheaper and it is a false economy. Three differences matter.

• UV stabilisation. Horticultural film is treated to survive sunlight. Packaging wrap goes brittle and yellow, often within a single season, and then shatters into fragments you spend a spring picking out of your borders.
• Bubble size. Horticultural film uses larger cells — commonly around 20–30mm — which trap more air per layer and pass more light than the dense small-cell packaging material.
• Clarity. Horticultural grades are made to transmit light. Packaging wrap is made to protect a vase, and its optical properties are nobody's concern.

Triple-wall and twin-layer horticultural films exist and insulate better again, at further cost to light and price. For most hobby greenhouses, standard large-cell single-layer film on the right surfaces is the sweet spot.

Where the film goes, in priority order

1. The north-facing side. Contributes very little light in winter and leaks heat like everywhere else. Line it heavily and without guilt.
2. Both end walls. High surface area, high loss, low light contribution at winter sun angles.
3. The door. Usually the single worst-sealed part of the structure. Film plus a proper seal — see weatherstripping and door seals — is the cheapest improvement available.
4. The roof. Heat rises, so the roof is a genuine loss surface, but it is also your main winter light source. This is the judgement call. Line it if you are heating to a set minimum; leave it if you are growing salad through winter unheated.
5. The south-facing side. Last, and often not at all.

A partial approach that works well: line the whole house but only to bench height on the south side. You keep the light where it falls on plants and cut the draft at floor level where cold air pools.

Fixing it, by frame type

Aluminium frames

Purpose-made greenhouse clips push into the glazing channel and grip the film. They are the correct answer, they cost very little, and they leave no damage. Buy more than you think — every metre of edge wants a fixing every 30 to 40cm or the film sags and the trapped air pocket collapses.

Do not tape film directly to aluminium in cold weather. Tape adhesion on cold metal is poor, and the tape you do get to stick will fight you in spring.

Timber frames

Stainless staples, or better, thin timber battens screwed over the film edge. Battens spread the load, stop the film tearing at the staple points, and can be unscrewed and reused every year. This is the most durable installation of the three.

Polytunnels and film houses

Clip the bubble to the hoops with the same clips used for the outer film, or run a batten along the hoop line. Keep an air gap between the outer film and the bubble layer — the gap is doing real work, and film pressed flat against film insulates barely better than a single layer.

Thermal screens: the other half of the category

Bubble film is a fixed, all-day layer. A thermal screen is a movable horizontal layer pulled across at dusk and opened at dawn, which is the elegant solution to the light-versus-heat trade: full light by day, a trapped air ceiling by night.

Commercial growers run motorised screens. In a hobby house you can get most of the benefit with a simple wire-and-curtain-hook arrangement carrying a light film or fleece, drawn by hand. The catch is that it only works if you actually draw it every evening, which in practice means it works for people who are in the greenhouse daily and gathers dust for everyone else.

A screen at bench height rather than roof height is a further improvement, because you are only heating the volume the plants occupy rather than the whole roof space.

Measuring before you order

Film is sold by the roll in fixed widths. Measure the height of your side walls and the height and width of each end wall, then work out how your roll width maps onto those surfaces — running the film horizontally in bands often wastes far less than trying to run it vertically in full drops.

Add 10% for overlap. Panels should overlap at joins by several centimetres, otherwise you have a cold line running the height of the house at every seam.

Order the clips at the same time as the film. Ordering film, discovering you have no fixings, and taping it up "temporarily" is how most bad installations begin.

What to buy

Three installation mistakes worth avoiding

Fitting it to a dirty, wet frame

Clips slip, tape fails, and you seal a season of algae and spores in behind the film for the winter. Insulation goes up after the house is cleaned and while the frame is dry, which is why it sits at stage three of the fall changeover sequence rather than at the front.

Sealing the house completely

Insulation and airtightness are not the same thing, and a fully lined greenhouse with every vent taped shut is a gray mold factory. Keep at least one vent operable, keep air moving, and read autumn condensation and gray mold. Condensation running down the inside of bubble film is normal; standing water pooling in the bubble channels is a sign you have sealed too hard.

Leaving it up too long in spring

Come out in March. The light is worth more than the heat by then, and film left up through April costs you the early growth you insulated all winter to protect. Take it down, clean it, dry it fully and roll it — a good horticultural film gives several seasons if stored dry and out of sunlight.

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Common questions