Why Softness and Bulk Define Tissue Quality

In the tissue industry, two properties decide whether a product wins shelf space or gets returned: softness (hand feel) and bulk (thickness per unit weight). A tissue sheet that feels rough or collapses under light pressure fails the consumer test immediately. Yet many mills struggle to balance these two parameters because they are often inversely related — increasing one can compromise the other.

This article breaks down the five most influential process levers that tissue producers can adjust to simultaneously improve softness and bulk, drawing on established papermaking science and equipment design principles.

1. Fiber Selection and Furnish Blend

The starting point for any tissue grade is the fiber itself. Hardwood kraft fibers (eucalyptus, acacia, birch) are short, thin-walled, and collapse easily during pressing — producing dense, smooth sheets ideal for softness. Softwood kraft fibers (pine, spruce) are longer and stiffer, contributing strength and bulk but potentially reducing surface smoothness.

A typical premium tissue furnish blends 60-80% hardwood with 20-40% softwood. The exact ratio depends on the target balance between softness (hardwood-driven) and tensile strength (softwood-driven). Recycled fiber can be used for value grades, but it tends to be more heterogeneous and may require additional refining to achieve acceptable formation.

Key takeaway: Audit your incoming fiber quality regularly. Variations in species mix, storage time, or pulping conditions will cascade through every downstream process.

2. Refining Intensity and Specific Edge Load

Refining is where many tissue mills lose control of bulk. The goal in tissue refining is fibrillation without cutting — you want to develop fiber bonding area for strength while preserving fiber length for bulk. This requires low-intensity refining with a specific edge load (SEL) typically in the range of 0.8–1.5 W·s/m for hardwood and 1.5–2.5 W·s/m for softwood.

Disc refiners with wide plate gaps and fine bar patterns are preferred. Dummy head or conical refiners running at low specific energy input (30–60 kWh/t for hardwood) help maintain fiber length. Over-refining collapses fibers, reduces bulk, and wastes energy — tissue mills that refine above 80 kWh/t on hardwood are almost certainly overdoing it.

Operational tip: Measure freeness (CSF) at the refiner outlet at least twice per shift. A drop of more than 50 mL CSF without intentional process change signals refiner plate wear or feed consistency drift.

3. Headbox Consistency and Jet-to-Wire Ratio

Tissue forming depends on extremely low headbox consistencies — typically 0.10–0.25% for crescent formers and 0.15–0.35% for suction breast roll formers. At these dilutions, even small fluctuations in fan pump output or white water consistency cause visible formation defects.

The jet-to-wire ratio controls fiber orientation. A ratio close to 1.0 produces a more random sheet with better bulk and CD tensile, while ratios above 1.05 orient fibers in the machine direction, increasing MD tensile at the expense of CD properties and bulk. For premium tissue targeting softness, maintain jet-to-wire ratio at 0.98–1.02.

4. Yankee Dryer Coating and Creping Chemistry

The Yankee coating package is the single most powerful lever for sheet softness. A well-formulated coating — typically a blend of release agents, modifiers, and sometimes strength additives — controls both adhesion and release. If adhesion is too strong, the sheet tears at the creping blade. Too weak, and creping is ineffective, producing a flat, boardy sheet.

Creping blade geometry matters equally. A blade bevel angle of 85–95° combined with a creping pocket angle of 15–25° produces fine, dense crepe folds that maximize softness. The crepe ratio (reel speed / Yankee speed) typically ranges from 1.15 to 1.30 for premium bath tissue — higher ratios increase bulk and softness but reduce machine efficiency.

5. Through-Air Drying (TAD) vs. Conventional Drying

TAD technology represents the gold standard for bulk and softness, but many mills operate conventional dry-crepe machines. On conventional machines, bulk after the Yankee is largely determined by creping conditions. On TAD machines, the through-air drying step preserves the three-dimensional structure of the sheet formed on the TAD fabric — this is why TAD tissue can achieve bulk levels 50-80% higher than conventional tissue at the same basis weight.

For mills upgrading from conventional to structured tissue (Atmos, NTT, eTAD), the critical equipment considerations include vacuum dewatering capacity, TAD cylinder temperature profiling, and fabric selection.

Integrating Equipment Design for Consistent Results

Achieving target softness and bulk month after month requires more than individual parameter tweaks — it demands integrated equipment designed for tissue-specific process windows. Headboxes with precision dilution control, refiners with accurate gap measurement, and Yankee coating systems with automated chemical dosing all contribute to the repeatability that tissue converters demand.

For tissue producers evaluating capacity upgrades or new lines, the equipment selection process should prioritize machines with proven consistency in the 0.10–0.30% headbox range and Yankee sections designed for the specific creping chemistry your furnish requires.

📧 Contact our engineering team for a technical discussion of your tissue machine requirements: leizhanzhang@gmail.com