Key takeaways
Short answer: Pull means downstream demand pulls work and upstream produces only on a signal. Kanban caps work-in-process at each step with cards; CONWIP caps total WIP across the whole line. Kanban produces a smoother, more even workload; CONWIP produces higher throughput at higher WIP variance. The choice depends on whether even workload or maximum output matters more. See also oee for manufacturing.
A pull system signals production from downstream consumption rather than pushing it from an upstream schedule. Nothing is made until something is taken, which directly attacks overproduction — the worst of the seven wastes — because the system only ever replaces what was used.
Kanban caps WIP at each individual step using cards. A step can only work when it holds a card, and a card returns only when the downstream step consumes its output. This gives tight, local control and a very even workload across stations.
CONWIP (constant work-in-process) caps total WIP across the whole line rather than per step. When a finished unit exits, a new unit may enter. The bottleneck balances the line naturally, and throughput is typically higher, at the cost of more WIP variance upstream.
A line with an uneven bottleneck runs kanban: each step is capped, so workload is smooth and predictable, but the bottleneck is sometimes starved by the rigid per-step caps and throughput suffers slightly. Switch to CONWIP — cap total WIP, let work flow to wherever it is needed up to the limit — and the bottleneck stays fed, lifting throughput, but WIP now pools unevenly in front of it. Same line, same pull principle: kanban optimised smoothness, CONWIP optimised output.
Kanban gives smoother flow, lower variance and slightly lower throughput — good for stable demand, multiple product types with separate loops, and where even workload matters. CONWIP gives higher throughput at higher WIP variance — good for variable demand and bottleneck-dominated lines where output is the priority.
1. Calling MRP "pull." MRP is push — it plans from forecast.
2. Kanban without sized buffers. Stockouts or overproduction result.
3. CONWIP without identifying the bottleneck. The system floods upstream of the constraint.
4. Never reviewing the WIP caps. Caps go stale as demand changes.
Pull systems affect OEE Performance (smoother flow, fewer micro-stoppages) and Availability (less starvation at the bottleneck). Whether kanban or CONWIP serves you better shows up in how cleanly the constraint stays fed and how steadily the line runs.
Fabrico visualizes WIP, queue and starvation station by station, so you can see whether kanban or CONWIP is keeping your bottleneck fed. Book a demo to see flow and WIP in your data.
Both are pull systems, but CONWIP caps total WIP while kanban caps it per step.
Yes — hybrid systems are common, matching the method to each part of the line.
CONWIP usually, by keeping the bottleneck fed.
Kanban, through tight per-step WIP caps.
No — MRP is push; it plans from forecast, not consumption.
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