Testing standard
Tissue paper and tissue products — Part 4: Determination of tensile strength, stretch at maximum force and tensile energy absorption; and Part 5: Determination of wet tensile strength
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 12625-4 determines the dry tensile strength, stretch at maximum force and tensile energy absorption of tissue paper and tissue products; ISO 12625-5 determines the wet tensile strength of the same materials after soaking. Both stretch a 50 mm wide strip to break at a constant rate of elongation, and results are reported separately for the machine and cross directions. The current editions are ISO 12625-4:2022 and ISO 12625-5:2024, both third editions.
A strip of tissue 50,0 ± 0,5 mm wide is clamped across its full width at each end and stretched to break at a constant rate of elongation. Part 4 does this on conditioned dry tissue over a 100 ± 1 mm span at 50 mm/min — the rate is 50 % of the initial span per minute, so a shortened 50 mm span runs at 25 mm/min. Part 5 does the same on tissue just wetted. On a vertical machine the strip is looped under the rod of a Finch Cup soaking device held in the lower clamp, the water container rises to immerse the rod 20 ± 1 mm deep, and after 15 s it drops away and the pull begins at 50 ± 2 mm/min. A horizontal machine uses a soaking device placed between the clamps instead.
Part 4 reports tensile strength in newtons per metre, stretch at maximum force as a percentage, and tensile energy absorption — the area under the force–elongation curve per unit area, the closest single figure to the work a sheet absorbs before giving way. Dividing the first and last by grammage gives the tensile index and the tensile energy absorption index, so a light sheet compares fairly with a heavy one. Part 5 reports wet tensile strength and, against a dry result from the same sample, wet-tensile-strength retention. For a kitchen towel or a moist wipe that ratio is the product: a sheet strong dry that collapses wet fails in the hand. Results are reported separately for machine and cross direction, because tissue is strongly anisotropic and one averaged number hides the direction that will actually tear.
Both parts use the same strip. What differs is how many are taken and what happens to them before the pull.
Results are calculated and reported separately for the machine and cross direction. Tissue is strongly anisotropic, and one averaged figure hides the direction that will actually tear.
S = (F / w) × 10³
Reported to three significant figures. Because the width is fixed, a tissue result is a force per unit width, not a stress.
I = S / g
Dividing by grammage is what lets a light sheet be compared fairly with a heavy one.
A = (ε / l) × 100
Reported to the first decimal place.
Z = E / (w × l) × 1 000
The area is taken up to the point of maximum force, not to break. It is the closest single figure to the work a sheet absorbs before giving way.
I₂ = Z / g
Wet tensile strength as a percentage of the dry
The two figures come from different test pieces out of the same sample, not from the same piece tested twice. For a kitchen towel or a moist wipe this ratio is the product.
If more than 20 % of the pieces cut from a specimen break at the clamping line — or on the rod, under Part 5 — reject every reading from that specimen and inspect the apparatus before going on. The rule exists because a jaw problem produces plausible low numbers rather than an obvious fault.
The choice that decides whether the test is possible at all. Part 4 requires the force measurement to be accurate to ±1 % of reading or ±0,025 N, whichever is greater — a cell chosen for the frame rather than for tissue cannot see that floor.
Specifications
Air-driven vice action for paper and tissue, with the clamping force adjustable — which the method requires, because it caps clamping at 0,25 N. Both parts also need a clamp at least 50 mm wide gripping along a straight line across the full width of the piece, so the faces are specified to the test piece rather than taken as standard.
SpecificationsVery little force, resolved very finely. The force-measuring system must be accurate to ±1 % of reading or ±0,025 N, whichever is greater, and verified to ISO 7500-1; the apparatus must conform to ISO 1924-2. That 0,025 N floor decides the machine, because a load cell sized for the frame rather than for tissue cannot see it. Elongation is recorded to ±0,1 mm and does not begin counting until 0,25 ± 0,05 N, the slack correction. Clamps must be at least 50 mm wide, grip along a straight line across the full width without damaging the sheet, and stay parallel within 1°. Tensile energy absorption needs the area under the curve to within ±2 %. Under Part 5 the lower clamp holds the Finch Cup, not a specimen.
Clamping too hard. Part 4 caps the clamping force at 0,25 N for a reason: tissue crushed at the jaw breaks at the jaw. Breaks within 5 mm of the clamping line are discarded under Part 4, and within 2 mm of the upper clamp or on the rod under Part 5; if more than a fifth of a specimen's pieces fail that way the whole set is rejected and the apparatus inspected. Touching the test area puts moisture and oil into a sheet weighing grams per square metre; skipping conditioning moves every result at once. On wet tests, an overrun soak or a rod left damp between pieces both push the numbers the same way, and neither leaves a trace.
| ISO 12625-4 | ISO 12625-5 | ISO 1924-2 | |
|---|---|---|---|
| Material | Tissue, dry | Tissue, soaked | Paper and board |
| Rate | 50 % of the span per minute | (50 ± 2) mm/min | 20 mm/min |
| Test span | (100 ± 1) mm | (50 ± 1) mm, looped | As specified for paper |
| Wetting | None | Finch Cup or trough, 15 s | None |
| Reports | Strength, stretch, TEA and the indices | Wet strength, and retention against a dry result | Tensile properties of paper |
ISO 1924-2 is the parent apparatus specification that both tissue parts point back to, but it is not a substitute for either: it runs at a different rate on a different material, so a paper result and a tissue result are not interchangeable figures.
It is the international method for the dry tensile properties of tissue paper and tissue products. A strip (50,0 ± 0,5) mm wide is stretched to break over a (100 ± 1) mm span at a constant rate of elongation, and the method reports tensile strength in newtons per metre, stretch at maximum force as a percentage, and tensile energy absorption, plus the tensile index and tensile energy absorption index calculated against grammage. The current edition is ISO 12625-4:2022, the third, which cancels the withdrawn 2016 edition.
It is the companion method for wet tensile strength, currently ISO 12625-5:2024. The same strip is soaked with water immediately before the pull rather than tested dry. On a vertical machine the piece is looped under the rod of a Finch Cup soaking device held in the lower clamp, the water container is raised so the rod is immersed to (20 ± 1) mm, and after 15 s it drops away and the pull begins at (50 ± 2) mm/min. A horizontal machine uses a soaking device placed between the clamps instead.
The wet tensile strength expressed as a percentage of the dry tensile strength of a different test piece from the same sample, conditioned to ISO 187. It is the number that matters commercially for anything meant to be used wet: a sheet that is strong dry and collapses when wetted fails in the hand, and only the ratio shows that. Note that it compares two different test pieces from one sample rather than one piece tested twice.
Because tissue is strongly anisotropic — the fibres orient with the machine direction, and the two directions can differ by a large factor. Both parts require the results to be calculated and reported separately for each direction. A single averaged figure hides whichever direction is weaker, which is the direction that will tear in service.
A low-range one, chosen for the specimen. Part 4 requires the force-measuring system to be accurate to ±1 % of the reading or ±0,025 N, whichever is greater, verified to ISO 7500-1, and the apparatus to conform to ISO 1924-2. That 0,025 N floor is the specification that decides the machine: a cell sized for the frame's capacity rather than for a few newtons of tissue simply cannot resolve the result.
Because tissue crushed at the jaw breaks at the jaw. Part 4 states that the test piece shall not be clamped with a force greater than 0,25 N, which is 5 N/m across the 50 mm width, and requires the clamps to have a means of adjusting that force. The clamps must also be at least 50 mm wide and grip along a straight line across the full width without damaging the sheet, with the clamping lines parallel within 1°.
They are discarded and replaced. Under Part 4 a break within 5 mm of the clamping line does not count; under Part 5 the exclusion is a break within 2 mm of the upper clamp or on the rod. Testing continues until 10 valid results are available in each direction. If more than 20 % of the pieces cut from one specimen break that way, every reading from that specimen is rejected and the apparatus is inspected — the pattern points at the grips rather than the tissue.
It is a heat treatment, also called curing or rapid ageing, that develops the strength a wet-strength agent would otherwise reach over weeks of natural ageing. Part 5 gives (80 ± 2) °C for 30 min followed by at least an hour of conditioning, or (105 ± 2) °C for 15 min where production data are needed quickly. It is optional and the user decides, but the report has to state whether it was done and by what procedure, because an aged and an unaged result are not comparable.
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Very low, and resolution decides the machine rather than capacity. The force-measuring system must be accurate to ±1 % of the reading or ±0,025 N, whichever is greater; a load cell sized for the frame cannot see a tissue result. No specimen force range is quoted, none having been corroborated twice. | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ISO 7500-1; force accurate to ±1 % of reading or ±0,025 N, whichever is greater | ISO 7500-1 Class 0.5 — a class tighter than the method asks |
| Gripping | Clamps at least 50 mm wide gripping along a straight line across the full width, with adjustable clamping force not greater than 0,025 N placeholder | Our a fixture built for this method, built to the specimen |
| Environment | ISO 187 standard atmosphere for paper, board and pulps — conditioning before the test pieces are cut, and maintained throughout | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
