HFO 40 Closed-Cell Spray Foam | Rayston HFO Spray Foam Insulation
Contents
- What is HFO 40 spray foam and when should you specify it?
- HFO blowing agent and two-component system make-up
- Applied foam properties: density, closed cells, λ, μ, water absorption and fire
- Aged thermal performance table (thickness / λ / R)
- Mix ratios and site application conditions
- Component properties and laboratory reactivity
- Safety, storage, equipment cleaning and empty containers
- HFO 40 vs other Rayston grades: which one to choose?
- HFO 40 spray foam: FAQ
- Engineering summary
- Related links
Rayston Spray Foam HFO 40 by Krypton Chemical: an HFO-blown rigid closed-cell spray foam with 42–47 kg/m³ density, λ = 0.028 W/m·K and closed cells > 90% — figures from the technical datasheet.
- Product: Rayston Spray Foam HFO 40
- Grade: HFO 40
- Application: spray-applied thermal insulation
HFO 40 spray foam (Rayston Spray Foam HFO 40) is a two-component rigid spray polyurethane foam system from Krypton Chemical, S.L., designed for spray-applied thermal insulation of vertical walls and interior ceilings where the surface is not subject to permanent loads. It is blown with HFO (trans-1-chloro-3,3,3-trifluoropropene) and has an applied density of 42–47 kg/m³, declared thermal conductivity λ = 0.028 W/m·K and closed-cell content > 90%, according to the official technical datasheet (last revised 02/06/2026).
This article covers one grade of the Rayston Spray Foam range. To compare all grades, see the general guide: spray polyurethane foam.
01
What is HFO 40 spray foam and when should you specify it?
HFO 40 spray foam (Rayston Spray Foam HFO 40) is a rigid polyurethane foam made from a two-component system (polyol + isocyanate). It is sprayed directly onto the substrate to form a continuous, fully adhered insulation layer that limits thermal bridging at corners and joints.
Use declared in the datasheet:
- Spray-applied thermal insulation on surfaces not subject to permanent loads, such as vertical walls and ceilings from the inside.
- On façades: repels water while still allowing the construction to breathe to some degree.
According to the official technical datasheets, the product contains no fibres and no biohazardous materials. It is intended for industrial and professional use only and is not suitable for DIY.
Manufacturer: kryptonchemical.com.
Internal links: Knowledge base · Products · Documents.
02
HFO blowing agent and two-component system make-up
HFO 40 spray foam is blown with HFO, specifically trans-1-chloro-3,3,3-trifluoropropene. This places it in the HFO family of the Rayston line (alongside HFO 35 and HFO 50), as opposed to the water-blown grades (30W / 40W / 50W) and the 8W open-cell grade.
From an engineering standpoint, the HFO family in this range is associated with:
- Declared closed-cell content > 90%.
- Declared thermal conductivity of 0.028 W/m·K (for both HFO 35 and HFO 40).
- Water vapour diffusion resistance factor μ ≥ 80.
Designation code according to the datasheet:
PU EN 14315-1-ccc4-CT3 (20)-TFT18(20)-FRB40(20)-W0,2-MU80
The reference standard for use as thermal insulation in buildings (ThIB) is EN 14315-1:2013, together with guidance document NB-CPR/SG19-17/167r2 dated 24/01/18.
03
Applied foam properties: density, closed cells, λ, μ, water absorption and fire
Applied density
42–47 kg/m³
UNE EN 1602
Closed-cell content
> 90%
Reaction to fire
Class E (all thicknesses)
UNE-EN 13823:2002
| Property | Value | Standard / TDS reference |
|---|---|---|
| Applied density | 42–47 kg/m³ | UNE EN 1602 |
| Free-rise density (lab) | 31–35 g/L | EN 14315-1:2013 |
| Closed-cell content | > 90% | — |
| Declared thermal conductivity λ | 0.028 W/m·K | UNE-EN 12.667 |
| Reaction to fire | Class E (all thicknesses) | UNE-EN 13823:2002 |
| Short-term water absorption | ≤ 0.2 kg/m² | EN 14315-1:2013 |
| Water vapour diffusion resistance factor μ | ≥ 80 | EN 14315-1:2013 |
Brief engineering notes:
- An applied density of 42–47 kg/m³ places this grade between HFO 35 (30–40) and HFO 50 (48–55) within the HFO family.
- No numerical compressive strength is given for HFO 40 in the datasheet.
- Reaction to fire is declared as Class E for all thicknesses, and the CE marking block states that reaction-to-fire performance does not deteriorate over time.
04
Aged thermal performance table (thickness / λ / R)
Base the project’s thermal calculation on the target-thickness row of the datasheet’s aged performance table, not on the general declared value alone. For HFO 40 spray foam, λ = 0.028 from 30 to 75 mm, then drops to 0.027 from 80 to 115 mm and to 0.026 from 120 to 200 mm, while thermal resistance R rises in proportion to thickness.
R (m²·K/W)
Aged λ (W/m·K) 0.028 · thickness 30–75 mm
30 mm
1.05
35 mm
1.25
40 mm
1.40
45 mm
1.60
50 mm
1.80
55 mm
1.95
60 mm
2.15
65 mm
2.30
70 mm
2.50
75 mm
2.70
Aged λ (W/m·K) 0.027 · thickness 80–115 mm
80 mm
3.00
85 mm
3.20
90 mm
3.40
95 mm
3.55
100 mm
3.75
105 mm
3.95
110 mm
4.15
115 mm
4.30
Aged λ (W/m·K) 0.026 · thickness 120–200 mm
120 mm
4.70
125 mm
4.90
130 mm
5.10
135 mm
5.30
140 mm
5.45
145 mm
5.65
150 mm
5.85
155 mm
6.05
160 mm
6.25
165 mm
6.45
170 mm
6.65
175 mm
6.85
180 mm
7.05
185 mm
7.25
190 mm
7.45
195 mm
7.65
200 mm
7.85
Worked example: at 50 mm the grade achieves R = 1.80 m²·K/W at λ = 0.028. At 100 mm this becomes R = 3.75 with λ = 0.027, and at 200 mm it reaches R = 7.85 with λ = 0.026.
| Thickness (mm) | Aged λ (W/m·K) | R (m²·K/W) |
|---|---|---|
| 30 | 0.028 | 1.05 |
| 35 | 0.028 | 1.25 |
| 40 | 0.028 | 1.40 |
| 45 | 0.028 | 1.60 |
| 50 | 0.028 | 1.80 |
| 55 | 0.028 | 1.95 |
| 60 | 0.028 | 2.15 |
| 65 | 0.028 | 2.30 |
| 70 | 0.028 | 2.50 |
| 75 | 0.028 | 2.70 |
| 80 | 0.027 | 3.00 |
| 85 | 0.027 | 3.20 |
| 90 | 0.027 | 3.40 |
| 95 | 0.027 | 3.55 |
| 100 | 0.027 | 3.75 |
| 105 | 0.027 | 3.95 |
| 110 | 0.027 | 4.15 |
| 115 | 0.027 | 4.30 |
| 120 | 0.026 | 4.70 |
| 125 | 0.026 | 4.90 |
| 130 | 0.026 | 5.10 |
| 135 | 0.026 | 5.30 |
| 140 | 0.026 | 5.45 |
| 145 | 0.026 | 5.65 |
| 150 | 0.026 | 5.85 |
| 155 | 0.026 | 6.05 |
| 160 | 0.026 | 6.25 |
| 165 | 0.026 | 6.45 |
| 170 | 0.026 | 6.65 |
| 175 | 0.026 | 6.85 |
| 180 | 0.026 | 7.05 |
| 185 | 0.026 | 7.25 |
| 190 | 0.026 | 7.45 |
| 195 | 0.026 | 7.65 |
| 200 | 0.026 | 7.85 |
05
Mix ratios and site application conditions
Mix ratio by volume (polyol : isocyanate)
100:100
Mix ratio by weight
100:110
Component temperature
30–60 °C
Working pressure
60–120 bar
Ambient temperature
0 to 40 °C
Relative air humidity
< 90%
Wind speed
< 30 km/h
Substrate temperature
5–40 °C
Substrate moisture
No surface condensation
| Condition | Value in the HFO 40 datasheet |
|---|---|
| Mix ratio by volume (polyol : isocyanate) | 100:100 |
| Mix ratio by weight | 100:110 |
| Component temperature | 30–60 °C |
| Working pressure | 60–120 bar |
| Ambient temperature | 0 to 40 °C |
| Relative air humidity | < 90% |
| Wind speed | < 30 km/h |
| Substrate temperature | 5–40 °C |
| Substrate moisture | No surface condensation |
Apply with dedicated spray equipment at the mix ratios above. The manufacturer’s recommendations do not relieve the applicator of reviewing the application method and running preliminary trials whenever there is doubt about the system’s suitability for site conditions.
06
Component properties and laboratory reactivity
The following values are given at 20 °C in the datasheet section on supplementary component information and reactivity:
Hydroxyl value
Polyol: 180–220 mg KOH
DIN-53240-2
Water content
Polyol: 2%
ISO-14.897
Viscosity
Polyol: 300–600 mPa·s
Isocyanate: 180–250 mPa·s
INT-IT-17
NCO content
Isocyanate: 30–32%
UNE-92120-1
| Property | Polyol | Isocyanate | Standard |
|---|---|---|---|
| Hydroxyl value | 180–220 mg KOH | — | DIN-53240-2 |
| Water content | 2% | — | ISO-14.897 |
| Viscosity | 300–600 mPa·s | 180–250 mPa·s | INT-IT-17 |
| NCO content | — | 30–32% | UNE-92120-1 |
| Cream time | 4 ± 1 s | EN 14315-1:2013 | |
| Thread (string) time | 11 ± 1 s | EN 14315-1:2013 | |
| Free-rise density | 31–35 g/L | EN 14315-1:2013 |
These are reference laboratory times; working times on site depend on component temperature, pressure and ambient conditions within the ranges above.
07
Safety, storage, equipment cleaning and empty containers
Occupational safety
Component B of HFO 40 spray foam contains isocyanates. Always follow the safety data sheet (MSDS): good ventilation and/or respiratory protection (organic vapour + particulate filters) together with protective clothing. Use the product only for the applications described in the datasheet; it is for industrial and professional use and not suitable for DIY.
Storage
Store both components between 10 and 25 °C, protected from moisture ingress. Under suitable storage conditions and in the original packaging, the maximum shelf life is 6 months from the date of manufacture.
Equipment cleaning
After application, clean the machine carefully to avoid contaminating the next system. Solvents are discouraged for cleaning machine parts; a plasticiser-based cleaning fluid such as Rayston Fluid is preferred. Remove component B completely from any parts exposed to air and replace it with cleaning fluid.
Empty containers and environment
Handle empty containers with the same precautions as full ones and hand them over as hazardous waste to a licensed waste manager. A and B can be mixed 1/1 to obtain an inert material, provided the quantity does not exceed 5 litres, to avoid a dangerous build-up of heat. Do not mix residues with any other product without knowing the possible reactions.
08
HFO 40 spray foam vs other Rayston grades: which one to choose?
Choosing a grade is a design decision driven by the application, density, λ, μ and any declared compressive requirements — not by the trade name alone. Within what the HFO 40 datasheet figures support:
1
You need closed cells > 90%, declared λ 0.028 and μ ≥ 80 within the HFO family, with an applied density of 42–47 kg/m³ → HFO 40 is the direct candidate.
2
Lower density within the same HFO family (30–40 kg/m³) → see HFO 35 spray foam.
3
Higher density, with a compressive strength > 200 kPa stated in the datasheet → see HFO 50.
4
Water-blown instead of HFO at similar densities → compare 40W (38–42 kg/m³, λ = 0.031, μ ≥ 70) via the general guide.
5
Declared sound insulation + lightweight open cells → 8W, not HFO 40.
This section does not replace a thermal calculation for the building, nor the technical datasheet of the selected grade. For the full side-by-side comparison of all grades, see the spray polyurethane foam guide.
09
HFO 40 spray foam: FAQ
What is HFO 40 spray foam, in short?
A two-component rigid polyurethane foam system (Rayston Spray Foam HFO 40) from Krypton Chemical, HFO-blown, with an applied density of 42–47 kg/m³, for spray-applied thermal insulation on surfaces not subject to permanent loads.
What is the declared thermal conductivity?
λ = 0.028 W/m·K to UNE-EN 12.667. In the ageing table, λ drops to 0.027 and then 0.026 at greater thicknesses; use the target-thickness row.
Is HFO 40 spray foam closed-cell?
Yes. Closed-cell content is declared as > 90% in the datasheet.
What is the correct mix ratio?
100:100 by volume and 100:110 by weight (polyol : isocyanate).
Is it suitable for permanent loads?
No, according to the datasheet wording: application on surfaces not subject to permanent loads (typically vertical walls and interior ceilings). Any use outside this scope requires an independent engineering decision.
What is the reaction-to-fire classification?
Class E for all thicknesses, according to UNE-EN 13823:2002.
Can it be applied as a DIY job?
No. The product is for industrial/professional use only and is not suitable for DIY.
Where can I compare HFO 40 with 40W, HFO 35 and HFO 50?
In the spray polyurethane foam guide, then in the grade articles: 40W spray foam, HFO 35 spray foam and HFO 50 spray foam.
10
Engineering summary
HFO 40 spray foam (Rayston Spray Foam HFO 40) is a rigid, HFO-blown grade in Krypton Chemical’s Rayston line: applied density 42–47 kg/m³, closed cells > 90%, declared λ of 0.028 with an ageing table that reaches 0.026 at high thicknesses, μ ≥ 80, short-term water absorption ≤ 0.2 kg/m² and reaction to fire Class E. Its declared use is spray-applied thermal insulation on surfaces not subject to permanent loads. Confirm the final choice against the datasheet figures and the project thickness, and refer to the general guide when comparing with the other grades.
11
Related links
General guide
Grade articles
HFO 40
Rayston Spray Foam HFO 40
| Grade | Trade name | Article |
|---|---|---|
| 8W | Rayston Spray Foam 8W | 8W spray foam |
| 30W | Rayston Spray Foam 30W | 30W spray foam |
| 40W | Rayston Spray Foam 40W | 40W spray foam |
| 50W | Rayston Spray Foam 50W | 50W spray foam |
| HFO 35 | Rayston Spray Foam HFO 35 | HFO 35 spray foam |
| HFO 40 | Rayston Spray Foam HFO 40 | This article |
| HFO 50 | Rayston Spray Foam HFO 50 | HFO 50 spray foam |
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