Specification

Zip opening, not zip length: specifying the opening on a makeup pouch

26 Oct 2026

Answer first: specify the usable opening, not the zip length. A zip bought as 20 cm gives a clear opening several centimetres shorter once end stops, seam allowance and the closed-end join are taken out, and it shortens again when the pouch is packed and the fabric bulges. Specify the tape length and you get a pouch a hand cannot get into.

Usable opening is the number for the drawing

Usable opening is the clear distance between the two end stops with the zip fully open, measured along the centre line. That is what the customer experiences. Put it on the drawing and let us work back to the tape length — not the other way round.

What eats the length

• End stops and the slider. Every zip has a fixed stop at each end, and the puller needs a clear run at the open end or it will not sit flat.
• Seam allowance at both ends. The opening is only as long as the part of the zip that is not sewn into the end seam.
• Binding or piping. Anything wrapped round the opening edge takes width off the clear gap.
• Contents. A full pouch pushes the two edges apart and the opening notices. Size it for the fullest the pouch will ever be, not for flat.

Straight or curved decides the zip type

A polished metal #3 zip will not follow a tight radius: the teeth are rigid, so the tape kinks and the slider drags. On a curved opening the working choice is a #5 nylon coil, because coils bend where cast teeth cannot. If the metal look is essential on a rounded pouch, the practical route is a straight metal opening on a rounded body: the shape of the pouch and the shape of the opening are two separate decisions.

Three questions we ask before cutting

• What goes in and out — a flat palette, a bottle 4 cm across, a brush handle?
• Does the pouch stand on a shelf or lie flat in a box? A flat pouch wants the zip along the top edge; a standing case usually wants one continuous coil round three sides.
• Where does the logo sit relative to the opening? Foil and print on the zip line get scuffed by the slider, and a deboss needs flat material with no seam running through it.

Confirm it on the sample

Opening, tape length and zip type are all confirmed on the first sample, with the actual contents inside. Sampling runs about 7 working days per round on stocked zips, and orders start at 3,000 pcs. Tell us what the pouch has to hold and we will size the opening from the contents.