HFO 35 Closed-Cell Spray Foam | Lightweight HFO Spray Foam by Rayston
Contents
- What is HFO 35 spray polyurethane foam and when should you specify it?
- HFO blowing agent and make-up of HFO 35 spray polyurethane foam
- Applied foam properties: density, closed cells, λ, μ, water absorption and fire
- HFO 35 spray foam 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 35 spray polyurethane foam vs other Rayston grades: which one to choose?
- HFO 35 spray polyurethane foam: FAQ
- Engineering summary
- Related links
Rayston Spray Foam HFO 35 by Krypton Chemical: an HFO-blown rigid closed-cell spray foam with 30–40 kg/m³ density, λ = 0.028 W/m·K and closed cells > 90% — figures from the technical datasheet.
- Product: Rayston Spray Foam HFO 35
- Grade: HFO 35 · closed-cell
- Application: spray-applied thermal insulation
HFO 35 spray polyurethane foam (Rayston Spray Foam HFO 35) is a two-component rigid SPF system from Krypton Chemical, S.L., sprayed directly onto vertical walls and ceilings from the inside 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 30–40 kg/m³, declared thermal conductivity λ = 0.028 W/m·K, closed-cell content > 90% and μ ≥ 80, according to the official technical datasheet (last revised 02/06/2026).
This article covers a single grade of the Rayston Spray Foam range (the HFO family). For a full comparison of all seven grades, see the general guide: spray polyurethane foam. Within the same family: HFO 40 spray foam and HFO 50 spray foam.
01
What is HFO 35 spray polyurethane foam and when should you specify it?
HFO 35 spray foam (Rayston Spray Foam HFO 35) is a rigid polyurethane foam made from a two-component system (polyol + isocyanate). Sprayed directly onto the substrate, it forms a continuous, seamless, fully adhered insulation layer that limits thermal bridging at corners and junctions.
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.
At 30–40 kg/m³, HFO 35 is the lightest grade of the HFO family, ahead of HFO 40 (42–47 kg/m³) and HFO 50 (48–55 kg/m³), while keeping the family’s defining properties: closed cells > 90% and a declared λ of 0.028.
According to the datasheet, the product contains no fibres and no biohazardous materials. It is for industrial and professional use only and not suitable for DIY.
Manufacturer: kryptonchemical.com.
Internal links: Knowledge base · Products · Documents.
02
HFO blowing agent and make-up of HFO 35 spray polyurethane foam
HFO 35 spray foam is blown with HFO, specifically trans-1-chloro-3,3,3-trifluoropropene, which places it in the HFO family of the Rayston line (alongside HFO 40 and HFO 50), as opposed to the water-blown grades (30W / 40W / 50W) and the 8W open-cell grade.
According to its datasheet, HFO 35 offers:
- Declared closed-cell content > 90%.
- Declared thermal conductivity of 0.028 W/m·K.
- Water vapour diffusion resistance factor μ ≥ 80.
Designation code according to the datasheet:
PU EN 14315-1-ccc4-CT3 (20)-GT11(20)-TFT18(20)-FRB32(20)-W0,2-MU80
Reference standard for use as thermal insulation in buildings (ThIB): EN 14315-1:2013, together with guidance document NB-CPR/SG19-17/167r2 dated 24/01/18. The CE marking block states that reaction to fire and compressive strength do not deteriorate over time, and that the declared thermal resistance accounts for ageing.
03
Applied foam properties: density, closed cells, λ, μ, water absorption and fire
Applied density
30–40 kg/m³
UNE-EN 1602
Closed-cell content
> 90%
— (row notes “does not allow water through”)
Reaction to fire
Euroclass E (all thicknesses)
UNE-EN 13823:2002
| Property | Value | Standard / TDS reference |
|---|---|---|
| Applied density | 30–40 kg/m³ | UNE-EN 1602 |
| Free-rise density (lab) | 32 g/L | EN 14315-1:2013 |
| Closed-cell content | > 90% | — (row notes “does not allow water through”) |
| Declared thermal conductivity λ | 0.028 W/m·K | UNE-EN 12667 |
| Reaction to fire | Euroclass 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 30–40 kg/m³ is the lightest in the HFO family, while retaining closed cells > 90% and code CCC4.
- λ = 0.028 matches HFO 40 and is lower than the water-blown grades (0.030–0.031).
- No numerical compressive strength is given in the HFO 35 sheet.
- Reaction to fire is Euroclass E for all thicknesses and, according to the CE marking block, does not deteriorate over time.
04
HFO 35 spray foam aged thermal performance table (thickness / λ / R)
Base the thermal calculation on the target-thickness row of the aged performance table, not on the general λ value alone. For HFO 35 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
2.95
85 mm
3.15
90 mm
3.35
95 mm
3.50
100 mm
3.70
105 mm
3.90
110 mm
4.10
115 mm
4.25
Aged λ (W/m·K) 0.026 · thickness 120–200 mm
120 mm
4.60
125 mm
4.80
130 mm
5.00
135 mm
5.20
140 mm
5.40
145 mm
5.60
150 mm
5.80
155 mm
5.95
160 mm
6.15
165 mm
6.35
170 mm
6.50
175 mm
6.70
180 mm
6.90
185 mm
7.10
190 mm
7.30
195 mm
7.50
200 mm
7.70
Worked example: at 50 mm, R = 1.80 m²·K/W with λ = 0.028; at 100 mm, R = 3.70 with λ = 0.027; and at 200 mm, R = 7.70 with λ = 0.026. Up to 75 mm the table matches HFO 40; beyond that, HFO 35 R values are slightly lower at greater thicknesses (7.70 vs 7.85 at 200 mm).
| 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 | 2.95 |
| 85 | 0.027 | 3.15 |
| 90 | 0.027 | 3.35 |
| 95 | 0.027 | 3.50 |
| 100 | 0.027 | 3.70 |
| 105 | 0.027 | 3.90 |
| 110 | 0.027 | 4.10 |
| 115 | 0.027 | 4.25 |
| 120 | 0.026 | 4.60 |
| 125 | 0.026 | 4.80 |
| 130 | 0.026 | 5.00 |
| 135 | 0.026 | 5.20 |
| 140 | 0.026 | 5.40 |
| 145 | 0.026 | 5.60 |
| 150 | 0.026 | 5.80 |
| 155 | 0.026 | 5.95 |
| 160 | 0.026 | 6.15 |
| 165 | 0.026 | 6.35 |
| 170 | 0.026 | 6.50 |
| 175 | 0.026 | 6.70 |
| 180 | 0.026 | 6.90 |
| 185 | 0.026 | 7.10 |
| 190 | 0.026 | 7.30 |
| 195 | 0.026 | 7.50 |
| 200 | 0.026 | 7.70 |
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 35 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 the system 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 on-site trials whenever there is doubt about the system’s suitability for the project 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
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 |
| Viscosity | 300–600 mPa·s | 180–250 mPa·s | INT-IT-17 |
| NCO content | — | 30–32% | UNE-92120-1 |
| Cream time | 3 ± 1 s | EN 14315-1:2013 | |
| Thread (string) time | 11 ± 1 s | EN 14315-1:2013 | |
| Drying (tack-free) time | 18 ± 1 s | EN 14315-1:2013 | |
| Free-rise density | 32 g/L | EN 14315-1:2013 |
These are reference laboratory times; working times on site depend on component temperature, working pressure and ambient conditions within the declared ranges. The HFO 35 sheet does not give the polyol water content.
07
Safety, storage, equipment cleaning and empty containers
Occupational safety
Component B of HFO 35 spray foam contains isocyanates, so always follow the safety data sheet (MSDS): good ventilation and/or respiratory protection (combined organic vapour and particulate filters) together with protective clothing. Use the product only for the applications described in the datasheet; it is intended for industrial and professional use and is not suitable for DIY.
Storage
Store both components between 10 and 25 °C, always 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 used on the same rig. Solvents are not recommended for cleaning machine parts; a plasticiser-based cleaning fluid such as Rayston Fluid is preferred. Remove component B completely from all 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. Never mix residues with any other product without knowing the possible reactions.
08
HFO 35 spray polyurethane foam vs other Rayston grades: which one to choose?
Choosing a grade is a design decision governed by the application, density, λ, μ and any declared compressive requirements — not by the trade name alone. Within the HFO 35 datasheet figures:
1
Closed cells > 90%, declared λ 0.028 and μ ≥ 80 with the lowest density in the family (30–40 kg/m³) → HFO 35 is the direct candidate.
2
The same properties at a higher density (42–47 kg/m³) → see HFO 40.
3
A stated compressive strength greater than 200 kPa in the datasheet → see HFO 50 (48–55 kg/m³).
4
5
Declared sound insulation with lightweight open cells → 8W, not HFO 35.
This section does not replace the building’s thermal calculation or the technical datasheet of the selected grade. For a side-by-side comparison of all seven grades, see the spray polyurethane foam guide.
09
HFO 35 spray polyurethane foam: FAQ
What is HFO 35 spray foam, in short?
A two-component rigid polyurethane foam system (Rayston Spray Foam HFO 35) from Krypton Chemical, HFO-blown, with an applied density of 30–40 kg/m³, for spray-applied thermal insulation on surfaces not subject to permanent loads.
What is the declared thermal conductivity of HFO 35 spray foam?
λ = 0.028 W/m·K to UNE-EN 12667. In the ageing table it drops to 0.027 and then 0.026 at greater thicknesses; use the target-thickness row.
Is HFO 35 spray foam closed-cell?
Yes. Closed-cell content is declared as > 90% in the datasheet, and the designation code carries ccc4.
What is the difference between HFO 35 and HFO 40 spray foam?
The core properties are similar (λ = 0.028, closed cells > 90%, μ ≥ 80), but HFO 35 is lighter (30–40 vs 42–47 kg/m³), its cream time is 3 ± 1 s, and its R values in the ageing table are slightly lower above 75 mm.
What is the correct mix ratio?
100:100 by volume and 100:110 by weight (polyol : isocyanate), with a component temperature of 30–60 °C and a working pressure of 60–120 bar.
Is it suitable for permanent loads?
No, according to the datasheet wording: the declared application is 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?
Euroclass E for all thicknesses, tested to UNE-EN 13823:2002; according to the CE marking block, reaction-to-fire performance does not deteriorate over time.
What is the shelf life and how should the components be stored?
Up to 6 months from the date of manufacture in the original packaging, with both components stored between 10 and 25 °C and fully protected from moisture.
10
Engineering summary
HFO 35 spray polyurethane foam (Rayston Spray Foam HFO 35) is the lightest grade in Krypton Chemical’s HFO family: applied density 30–40 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 Euroclass E. Its declared use is spray-applied thermal insulation on surfaces not subject to permanent loads. Settle the final choice against the datasheet figures and the project thickness, and refer to the general guide to compare it with the other grades.
11
Related links
General guide
Grade articles
HFO 35
Rayston Spray Foam HFO 35
| 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 | This article |
| HFO 40 | Rayston Spray Foam HFO 40 | HFO 40 spray foam |
| HFO 50 | Rayston Spray Foam HFO 50 | HFO 50 spray foam |
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