What's the main difference between VPM-B and Bühlmann?

Bühlmann (ZHL-16C) is a dissolved-gas model that limits supersaturation; VPM-B is a bubble model that limits bubble growth. VPM-B typically places deeper first stops.

Which one should I use?

Both are widely used and respected. Many divers run Bühlmann with gradient factors; others prefer VPM-B's deeper-stop profile. Choose with training and compare the two on the same dive.

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VPM-B vs Bühlmann — what's the difference?

These are the two decompression models technical divers argue about most. They start from different physics and produce differently-shaped ascents. Here's the plain-English version.

Bühlmann ZHL-16C — a dissolved-gas model

Bühlmann tracks dissolved nitrogen and helium across 16 tissue compartments and limits how supersaturated each one may become before you ascend. It's the model inside most dive computers. Conservatism is tuned with gradient factors (GF-low/GF-high). It tends to keep you slightly deeper than no-stop, then clear efficiently on the shallow stops.

VPM-B — a bubble model

VPM-B (Varying Permeability Model, with Boyle's-law compensation) assumes tiny gas bubbles always exist and limits how large they're allowed to grow. Because deep ascents let bubbles expand, VPM-B prescribes deeper first stops to control them early. Conservatism is set with levels +0 (least) to +5 (most) rather than gradient factors.

How the profiles differ

First stop: VPM-B usually starts deeper than a moderate gradient-factor Bühlmann plan.
Shallow stops: Bühlmann (especially with a low GF-high) tends to spend more time shallow.
Total runtime: often similar for the same dive — the time is just distributed differently.

Which should you use?

Both are well-established and respected; neither is "the safe one." The deep-stops debate has shifted over the years, and agencies differ. The practical answer: pick with proper training, and compare the two on the same dive to see how the schedule changes.

See them side by side

DecoLog runs both — switch between ZHL-16C + gradient factors and VPM-B (+0…+5) on the same plan and watch the stops change. Free.

Try it now — free, in your browser. • OPEN THE PLANNER

⚠ Educational only — not a substitute for training or a dive computer. Decompression diving requires certification; verify every plan independently.