Humidity, temperature, and dew point determine how your fountain pen writes today. NibFlow tells you which pen + ink + paper combo performs best — before you open the cap.
Live Example
Flow scores are estimates based on general ink behavior patterns. Actual performance varies by specific ink formulation, pen condition, and paper brand.
4-Axis Scoring
Will your nib dry out between strokes? EF nibs in dry heat need constant capping.
Will ink spread on the paper fibers? High humidity + wet ink = feathered edges.
How long before you can close the notebook? Shimmer ink on Tomoe River takes forever in humidity.
Will ink soak through to the back? B nibs + wet dye ink + cheap paper = guaranteed bleed.
Features
Absolute humidity, dew point, and wind speed — not just relative humidity. Same 60% RH behaves very differently at 10°C vs 35°C.
Register your pen + ink + paper combos. Free users get 1. Pro users get unlimited — ranked daily by flow score. (Pro)
See which days this week are ideal for your Pilot 823 EF. Plan ahead before opening a fresh bottle. (Pro)
Daily notification when any of your combos is rated Poor. Know before you sit down to write. (Pro)
Average flow score by pen, best and worst combos over time. See which setup really works for your climate. (Pro)
Tomoe River 52gsm vs 68gsm vs Rhodia vs Leuchtturm — each scored differently. Not just "premium" or "copy." (Pro)
Supported Ink Types
How It Works
Add your pen, ink type, wetness level, and paper. Takes 30 seconds.
Local humidity, temperature, dew point, and wind — fetched automatically each morning.
0–100 score across 4 axes. Pick the best combo for today and start writing.
Free to use. Pro features $4.99/month.
Download on the App Store