What cushion percentage should I run?

Run inside the window on your process sheet; Routsis Training suggests 5 to 10% of shot size. Check-ring variation alone moves cushion by 2 to 5% of the shot, so a smaller cushion can reach zero.

Why does my cushion change from shot to shot?

Mostly the check ring. Routsis puts normal check-ring variation during fill at 2 to 5% of shot size. DuPont notes that a leaking ring causes poor packing control and variable screw retraction time.

Can the cushion be too large?

Yes. Past your maximum, the melt left in front of the screw adds to the resin held in the barrel, which lengthens residence time for heat-sensitive resins.

How do I add cushion without changing the fill?

Add the same distance to the recovery end and transfer positions. The screw then meters and injects the same stroke, and the cushion grows by that distance, which this page reports as the shift.

Injection Molding calculator

Cushion Percentage Calculator

Check the cushion left at the end of hold against your minimum and maximum, as a share of shot size. You need the recovery end position and cushion from the controller's shot monitor.

What this calculator does

Cushion as a share of shot size, checked against your window, with the shift that brings it back.

Formula used

Shot size (mm) = recovery end position − cushion
Cushion percentage = cushion ÷ shot size × 100
Cushion at your minimum = minimum % × shot size ÷ 100; likewise for the maximum
Shift = MAX(cushion at minimum − cushion, 0) + MIN(cushion at maximum − cushion, 0)

Inputs explained

Recovery End Position: Screw position where recovery stops, before decompression.
Cushion: Screw position at the end of hold, from the shot monitor.
Minimum Cushion: Floor from your process sheet; Routsis suggests 5%.
Maximum Cushion: Ceiling from your process sheet; Routsis suggests 10%.

How to use the result

Best suited to setting cushion at mold qualification, resetting a job after a check-ring change, auditing a process sheet against shot monitor data.
A cushion inside the window can still drift; trend it over a run to catch a leaking check ring. Uses one cushion reading; enter the smallest from recent shots to judge the worst case.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 280.569 (BLS, Aug 2026), up 6.6% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 9,635 plastics product manufacturing establishments employing about 677,302 workers (Census County Business Patterns, 2023).

Common questions

What cushion percentage should I run? Run inside the window on your process sheet; Routsis Training suggests 5 to 10% of shot size. Check-ring variation alone moves cushion by 2 to 5% of the shot, so a smaller cushion can reach zero.
Why does my cushion change from shot to shot? Mostly the check ring. Routsis puts normal check-ring variation during fill at 2 to 5% of shot size. DuPont notes that a leaking ring causes poor packing control and variable screw retraction time.
Can the cushion be too large? Yes. Past your maximum, the melt left in front of the screw adds to the resin held in the barrel, which lengthens residence time for heat-sensitive resins.
How do I add cushion without changing the fill? Add the same distance to the recovery end and transfer positions. The screw then meters and injects the same stroke, and the cushion grows by that distance, which this page reports as the shift.

Related guides

Cushion Percentage as a Daily Process Health Check

Last reviewed 2026-10-01.