N-butane vs. isobutane vs. 70/30 butane/propane blends
Butane is not one thing. N-butane, isobutane and propane behave very differently in a cylinder and in a process, and blending them changes pressure and evaporation speed. Here is how they compare, using reference data from NIST.
Updated November 12, 2026 · Puretane
The three gases at a glance
| N-butane | Isobutane | Propane | |
| Normal boiling point | About 32°F (273 K) | About 12°F (262 K) | About −44°F (231 K) |
| Vapor pressure near 70°F | About 31 psia (about 16 psig) | About 46 psia (about 31 psig) | About 125 psia (about 111 psig) |
Boiling points from the NIST Chemistry WebBook for n-butane, isobutane and propane. Vapor pressures are NIST saturation-property values at about 21°C (70°F), rounded.
N-butane
N-butane is the straight-chain form. It has the highest boiling point of the three and the lowest pressure, so it is the gentlest to work with: it stays liquid longer and builds less pressure in a closed system. For solvent work, a high n-butane share with low sulfur, moisture and residue is what most buyers ask for. Puretane's 100% n-butane is lab-tested at 99.68% n-butane.
Isobutane
Isobutane is the branched isomer. It boils about 20°F lower than n-butane and runs at roughly twice the pressure at room temperature. It shows up in many consumer butane cans and in blends. When a CoA lists isobutane, that is not contamination; it is part of the hydrocarbon mix and should simply be reported.
Propane and 70/30 blends
Propane boils far colder and runs at many times the pressure of n-butane. Adding it to n-butane raises the blend's vapor pressure and makes it evaporate faster, which is why some processes prefer a blend. A 70/30 n-butane/propane mix is a common middle ground: noticeably more pressure than straight n-butane without the full pressure of propane. Puretane's 70/30 blend ships in 110 lb fills, and we can mix custom ratios such as 60/40 or 80/20 on request.
How to choose
- Lowest pressure, slower evaporation: straight n-butane.
- Faster evaporation, more pressure: a butane/propane blend; the more propane, the higher both go.
- Equipment limits come first: always stay within the pressure rating of your system and follow your equipment maker's guidance on solvent choice.
Not sure which ratio fits your process? Request a quote and tell us what you run; we will recommend a blend.
Frequently asked questions
Is isobutane the same as n-butane?
No. They have the same formula but different structures. Isobutane boils at about 12°F and runs at higher pressure; n-butane boils at about 32°F.
Why blend propane with butane?
Propane raises the vapor pressure and speeds up evaporation. A 70/30 n-butane/propane blend sits between straight n-butane and straight propane.
Can Puretane make other ratios?
Yes. Custom n-butane/propane blends such as 60/40 or 80/20 are available on request.