SuperFOIL SF19+ Insulation: What It Is, Where to Use It and How to Fit It
SuperFOIL SF19+ is a multi-layer (multifoil) insulation roll that does three jobs at once: it insulates, it works as a vapour control layer, and it reflects radiant heat. It comes up a lot when people are insulating lofts, rafters, sheds, garages, log cabins and floors, and it gets compared with PIR boards and mineral wool just as often. This guide explains what SF19+ is, what SuperFOIL and its independent assessors actually say about its performance, how to fit it, and when a different insulation is the better choice. We stock SF19+ in two widths, and everything below is taken from SuperFOIL's own datasheets and certification, not from marketing shorthand.
Quick answer
- What it is: a flexible 45mm roll of polyester wadding layers separated by reflective foil, faced with an aluminium foil vapour control layer. It is sold per roll in 1.2m x 10m and 1.5m x 10m sizes.
- Thermal performance: SuperFOIL quotes a core R-value of 1.63 m²K/W, rising to 2.53 (roof), 2.96 (wall) and 4.29 (floor) when it is fitted with two air spaces. Those higher figures only apply if the air gaps are built in properly.
- Best for: roofs, walls and floors where you want a light, easy-to-cut roll with a built-in vapour control layer, on awkward or uneven surfaces and in refurbishment, or as a layer combined with other insulation.
- Not the best for: spaces where depth is tight (the air gaps take room), open lofts where you just need thickness of wool, or jobs where you need a simple, predictable U-value from a single board.
- Fitting essentials: overlap joints by at least 50mm, tape every joint and cut edge with foil tape, staple at no more than 300mm centres, and leave the air gaps.
What is SuperFOIL SF19+?
SuperFOIL SF19+ is part of SuperFOIL's multifoil range, made by Boulder Developments in Lincoln. SuperFOIL describes it as a "3 in 1" product: insulation, vapour control layer and radiant barrier. The independent Kiwa BDA Agrément for the SF19+ internal wall system describes the roll as a blanket of eleven layers, made up of polyester fibre wadding layers separated by metallised foil layers, and faced with a reflective aluminium foil vapour control layer. The "19" in the name is a product code, not a layer count.
Key published details:
| Detail | SuperFOIL SF19+ |
|---|---|
| Nominal thickness | 45mm (sizes and figures are approximate and subject to tolerance) |
| Roll sizes | 1.2m x 10m (about 10kg) and 1.5m x 10m (about 13kg) |
| Emittance of the foil face | 0.05 |
| Water vapour resistance | 2,050 MNs/g (sd 410m), EN 1931 |
| Declared as | Vapour control layer to EN 13984, Class W1 for water penetration |
| Reaction to fire | Euroclass F in the declaration of performance (EN 13984). The Kiwa Agrément records Euroclass E for the product tested loose behind plasterboard in the wall system. |
| Recycled content | Up to 40% recycled material, according to SuperFOIL |
SuperFOIL's declaration of performance lists joint strength, resistance to impact, dangerous substances and chemical resistance as "NPD" (no performance determined), so there is no declared figure for those. It does declare tensile and tear resistance, which is why the roll copes with stapling and handling.
Sizes we stock
We list two SF19+ products, both sold per roll:
- SuperFOIL SF19+ 45mm, 1.2m x 10m: 12m² per roll before overlaps.
- SuperFOIL SF19+ 45mm, 1.5m x 10m: 15m² per roll before overlaps.
The rest of the range is on our Multifoil Insulation (SuperFOIL) collection, including SF19BB breathable, SF6 and SFUF underfloor foil. Choose the width that suits your rafter spacing, wall height or joist runs, so you cut and join as little as possible.
SF19+ R-values and U-values explained
Foil-based insulation is different from foam or wool because a lot of its performance comes from the air spaces either side of the foil, not only from the material. That is why SuperFOIL publishes two sets of numbers:
| Situation | R-value (m²K/W) | Source |
|---|---|---|
| Core value, no air spaces | 1.63 | SuperFOIL datasheet |
| Core value tested by Kiwa | 1.50 (thermal conductivity 0.035 W/mK) | Kiwa BDA Agrément BAW-24-342-S-A-UK |
| Roof, with two air spaces | 2.53 | SuperFOIL datasheet |
| Wall, with two air spaces | 2.96 | SuperFOIL datasheet |
| Floor, with two air spaces | 4.29 | SuperFOIL datasheet |
Two things to take from this. First, the headline figures with air spaces assume the gaps are there, at the right size, sealed and unventilated. Squash the roll tight against the plasterboard and you lose the benefit. Second, SuperFOIL's own published figures are not perfectly consistent: its SF19+ product page currently shows 2.60 (roof) and 3.11 (wall), while its datasheet and under-rafter page show 2.53 and 2.96. We have used the lower datasheet figures. If you need a figure for Building Control, ask SuperFOIL's technical team for a calculation for your build-up.
The U-value of a finished wall, roof or floor depends on everything in the build-up: the structure, any other insulation, timber bridging and the finish. The Kiwa Agrément gives one worked example: a solid brick wall with SF19+ compressed to 3.3mm between battens, a plasterboard lining and skim, which gives a U-value of 0.30 W/m²K. That is an example of a compressed installation, not a target. For anything that has to meet a specific U-value, ask SuperFOIL for a U-value and condensation calculation, or read our guide to R-values first.
Where SF19+ is used
Pitched roofs and lofts (under the rafters)
This is the most common use. SuperFOIL's under-rafter guide has you staple the roll to the underside of the rafters, working from the ridge down or running vertically from the high point, then fix counter-battens at no more than 600mm centres before the plasterboard or lining goes on. It is useful for loft conversions and room-in-roof spaces where you want a light roll that can follow awkward shapes. It is not a replacement for 270mm of mineral wool in an open, unheated loft; see what thickness of loft insulation you need.
Flat roofs (over the joists)
SuperFOIL also publishes an over-joist guide for flat roofs, where the roll is stapled over the joists, counter-battens or firrings are fixed through it, and the external finish goes on top. If you are thinking of a hybrid roof, with some insulation above and some below, SuperFOIL strongly advises talking to its technical team first because of the interstitial condensation risk.
Internal walls
The Kiwa Agrément covers SF19+ as an internal wall insulation system on masonry or solid walls: battens fixed to the wall at 600mm centres at most, SF19+ stapled on, overlaps taped, counter-battens over the top, then plasterboard. The Agrément expects walls to be sound and dry, a pre-installation survey and a condensation risk analysis, and installation by SuperFOIL-approved installers, so for a regulated wall retrofit speak to SuperFOIL and your Building Control body first.
Suspended timber floors
SuperFOIL's floor guide has SF19+ installed between the joists, under the floorboards, starting at the wall edge and lapped slightly up the wall, with the edge taped, and held in place with SuperFOIL spacers, staples or battens. Where rolls meet, SuperFOIL suggests overlapping by around 100mm and sealing with foil tape. Without extra insulation, it recommends a 50mm cavity above the roll for the best performance.
Sheds, garages, log cabins and outbuildings
SuperFOIL's literature covers roofs, walls and floors in new build and retrofit, and a shed, garage or cabin has the same three surfaces at a smaller scale. The same rules apply: build in the air spaces, tape the joints and make sure the structure stays dry. Our shed and garage insulation guide covers the wider job. SF19+ is also listed in our campervan insulation collection, but at 45mm it is a thick layer for a van, so check how much depth you have.
Tight spaces and awkward retrofits
It helps to be precise here. SF19+ is tight-space friendly in the sense of access and shape: it is a light roll you can carry through a small hatch and cut with a knife, shears or rotary cutter, and it follows irregular surfaces that rigid boards struggle with. It is not thin once you count the air gaps. If the limit is depth, rather than access, PIR will give you more R-value in less thickness (see the comparison below).
SF19+ vs PIR vs mineral wool
Here is an honest side-by-side. The "equivalent thickness" figures are simple arithmetic using R = thickness / conductivity, and we use a typical foil-faced PIR conductivity of about 0.022 W/mK and a typical glass wool loft roll of about 0.044 W/mK, so check the datasheet for the exact board or roll you choose.
| SuperFOIL SF19+ | PIR board (Celotex, Kingspan and others) | Mineral wool (loft roll or slab) | |
|---|---|---|---|
| Form | Flexible roll, cuts with a knife | Rigid foil-faced board | Soft roll, batt or slab |
| Performance | R 1.63 core, 2.53 roof, 2.96 wall, 4.29 floor with two air spaces | Fixed by thickness: about 36mm gives R 1.63, about 56mm gives 2.53, about 65mm gives 2.96 | Fixed by thickness: about 72mm of a 0.044 W/mK roll gives R 1.63; 270mm gives about R 6.1 |
| Depth needed | 45mm plus air spaces and battens | Just the board | Needs depth, but cheap to add |
| Vapour control | Built in when joints are taped | Foil facing, joints taped, but check the system | None, so a separate VCL may be needed |
| Handling | Light, easy to carry and cut, odd shapes are no problem | Rigid, needs accurate cutting and filling of gaps | Light, but itchy and dusty |
| Predictability | Depends on air gaps and workmanship | Predictable U-values from the datasheet | Predictable U-values from the datasheet |
| Best for | Awkward refurbs, combined build-ups, a roll with a built-in VCL | Tight depth, high R per mm, simple U-value calculation | Open lofts and between joists, lowest cost per R |
When SF19+ makes sense: uneven rafters or walls, hard-to-reach spaces, a refurbishment where you want a light roll with a vapour control layer included, or where you are layering it with another insulation in a build-up SuperFOIL has specified.
When PIR is better: you are short of depth, you want the most R-value per millimetre, or you need a straightforward U-value for Building Control. Read what thickness of PIR you need and our wool vs PIR vs foil comparison.
When mineral wool is better: an open loft, between ceiling joists, or anywhere you have the depth and want the lowest cost per unit of R-value. Our loft roll guide covers that case.
For the physics behind foil insulation, our guide to how reflective insulation works goes into more detail.
How to install SF19+
Follow SuperFOIL's installation guide for your application. The key points from the current guides are:
- Prepare the surface. It must be structurally sound, dry and free from damage. Check for asbestos-containing materials before you disturb anything in an older building, and deal with any damp first.
- Fix the first battens. SuperFOIL's roof guides list 38mm battens and 14mm staples for SF19+. This sets the air space on the room side, so use the specified size rather than whatever is to hand.
- Unroll and fix. Run the roll horizontally from the top down or vertically from the high point. Remove slack with gentle tension, then staple at no more than 300mm centres. Use galvanised or stainless staples.
- Overlap and tape. Overlap every joint by at least 50mm and seal it with foil tape (SuperFOIL specifies its own MultiFOIL tape). Seal cut edges, tears and penetrations as well. The vapour control job only works if the layer is continuous.
- Seal the edges. Seal to the wall plate, around windows and at junctions. At wall-to-roof junctions SuperFOIL asks for at least 50mm of overlap onto the wall so the insulation is continuous.
- Add counter-battens. Fix them over the roll at no more than 600mm centres. This forms the second air space under the lining.
- Finish. Fit the plasterboard or other lining. Do not leave the roll exposed for long.
Practical points: cut with a utility knife against a batten, a rotary cutter or heavy-duty shears. SuperFOIL will not support your weight, so do not walk on rolls laid over joists. Wrap copper pipes in a non-metallic material where they pass through, to stop them touching the aluminium. Keep the insulation away from flues and heat sources above 80°C, and do not fit it inside electrical outlets or junction boxes (Kiwa Agrément).
Common mistakes with multifoil
- Squashing out the air gaps. Without them you only get the core R-value, not the 2.53, 2.96 or 4.29 headline figures.
- Not taping joints and cuts. Untaped laps leak air and moisture and defeat the vapour control layer.
- Short overlaps. Under 50mm will not give a taped joint you can rely on.
- Wrong batten or staple size. It changes the air space and can mean staples that miss the timber or work loose.
- Loose, sagging fixing. Staples further apart than 300mm and slack in the roll make gaps and uneven air spaces.
- Fitting over damp. A vapour-tight layer over a damp wall or roof traps moisture. Fix the damp first and get a condensation risk check where needed.
- Using it as a like-for-like swap for 270mm of loft wool. It is not.
- Assuming a U-value. If you need a number for Building Control, get a calculation for your exact build-up.
- Under-ordering. Overlaps and cuts use up more than people expect (see below).
How many SF19+ rolls do I need?
A 1.2m x 10m roll covers 12m² and a 1.5m x 10m roll covers 15m², but only before overlaps. With a 50mm overlap, each run of 1.2m covers about 1.15m, so a roll gives roughly 11.5m² of finished coverage, and 1.5m rolls give about 14.5m². Add cuts at corners, eaves and openings and a sensible allowance is around 10% on the area. That is our rule of thumb, not a SuperFOIL figure.
Area to insulate x 1.10, divided by the roll area, rounded up:
| Area to insulate | 1.2m rolls (12m²) | 1.5m rolls (15m²) |
|---|---|---|
| 10m² | 1 | 1 |
| 20m² | 2 | 2 |
| 30m² | 3 | 3 |
| 40m² | 4 | 3 |
| 50m² | 5 | 4 |
| 60m² | 6 | 5 |
| 80m² | 8 | 6 |
| 100m² | 10 | 8 |
Worked example: a loft conversion with two roof slopes, each 4.5m up the rafter and 7m long, is 2 x 31.5 = 63m². Add 10%: 69.3m². That is 6 rolls of 1.2m (72m²) or 5 rolls of 1.5m (75m²). Also order foil tape and the right battens and staples. If you are not sure, our insulation calculator can help, or call us.
Frequently asked questions
Is SuperFOIL SF19+ a vapour control layer as well as insulation?
Yes. SuperFOIL declares SF19+ as a vapour control layer to EN 13984, with a water vapour resistance of 2,050 MNs/g, and the Kiwa Agrément says it performs as a VCL when the overlaps are sealed with SuperFOIL MultiFOIL tape. That only holds if the layer is continuous and taped.
What is the R-value of SF19+?
SuperFOIL quotes 1.63 m²K/W for the core, and 2.53 (roof), 2.96 (wall) and 4.29 (floor) with two air spaces. The Kiwa Agrément gives a tested thermal resistance of 1.50 m²K/W for the product itself.
Does SF19+ have independent certification?
The SF19+ internal wall system holds a Kiwa BDA Agrément (BAW-24-342-S-A-UK). SuperFOIL also supplies a declaration of performance for SF19+ as a vapour control layer under EN 13984. These cover specific uses and conditions, so ask SuperFOIL which document applies to your roof, wall or floor.
Can I use SF19+ instead of loft insulation?
Not in a simple open loft. For that, mineral wool to around 270mm is far better value. SF19+ is more at home under rafters in a converted loft, or in refurbishments where the build-up has been designed around it.
Can I use SF19+ in a shed, garage or log cabin?
Yes, on the same principles as a house: build in the air gaps, tape every joint and keep the structure dry. In unheated outbuildings, condensation is the main risk, so look at ventilation as well as insulation.
Which width should I choose, 1.2m or 1.5m?
Pick the one that fits your surface with the fewest joins. For long runs between rafters or up a wall, the wider roll often means fewer taped seams, while the 1.2m roll is easier in confined spaces.
Can I walk on it or cut it on site?
You can cut it with a utility knife, rotary cutter or heavy-duty shears and tape the cut edge. You cannot walk on it: SuperFOIL warns that it will not support a person's weight.
Do you deliver SF19+?
We deliver to England only. See our delivery information for how it works.
Order SuperFOIL SF19+
Order SF19+ in 1.2m x 10m or 1.5m x 10m rolls, or browse the whole SuperFOIL multifoil collection. Current trade prices are shown on each product page. We deliver to England only (see delivery information). Call us on 03330 908479 (Mon–Thu 8am–5pm, Fri 8am–12pm), email sales@insulationwarehousedirect.co.uk, or order online.
Sources: SuperFOIL SF19+ product page; SF19+ key features datasheet; SF19+ declaration of performance; Kiwa BDA Agrément BAW-24-342-S-A-UK; SuperFOIL under rafter installation guide; flat roof over joist guide; floor installation guide.