Specifying textiles the essential skill

The ability to specify linen correctly is an essential skill for textile rental businesses. The sector is becoming even more competitive as more launderers enter the market to broaden their customer base and to improve the range of services provided to a discerning and demanding clientele.

Many newcomers mistakenly work on the basis that price is the only detail that matters but buying the wrong quality linen can turn a potentially profitable contract into one that loses money for the laundry and sours its relations with the customer.

Purchasing and specifying linen is a skill.?It requires at least a basic of understanding of how textiles are manufactured and the impact that production methods can have on the linen’s life and how it will react to the laundry process.

The laundry must set out a full specification against which the supplier’s products can be measured.

Manufacturers can use many different processes to produce their textiles. These will be chosen according to the properties needed, which will depend on the customer’s application and specific requirements. The laundry’s buyer must be absolutely sure of what is needed.

Specifying linen correctly requires familiarity with the different terms used. Here are most common.

Fibre: This is the single hair or filament that is spun to form the yarn. The length of the fibre is referred to as the staple filament length. The longer the fibre, the greater the friction between the yarns when they are spun together. Yarns with a low twist can be weak because they just pull apart. Very fine fabrics often use long staple filament fibres. Coarser fabrics use shorter filament fibres twisted more tightly.

Yarn: This is what is produced when the fibres are twisted together. Yarns are interlaced on a loom to produce the fabric.

Warp yarns (or ends): These are the yarns that go down the length of the fabric.

Weft yarns (or picks): Yarns that go across the width.

The first step is to decide the fabric’s fibre content. This will depend upon the application.

The options include 100% natural fibres such as cotton, silk or wool, a 100% synthetic fibre such as nylon or polyester or mixtures of both types at different ratios, for example 50:50 polyester cotton or 77:30 cotton polyester.

Each fibre type will confer completely different properties to the finished fabric. A 100% polyester does not absorb moisture so it would not be suitable for drying kitchen items or for bathroom towels.

The next step is to decide how the chosen fibres are blended together. Some fabrics will use 100% polyester in all the warp yarns and 100% cotton in all the weft yarns, others will mix the yarns in various patterns such as alternating cotton or polyester in the warp or weft.

The manufacturer can also mix cotton and polyester fibres together into a single yarn. Proportions of each type will vary according to the requirements and this will affect the price.

The amount and type of fibre that goes into the yarn and the twist that is put into it can have a big impact on both the fabric’s life and its performance in the laundry. If the twist in the weft yarn is too low, the fabric can become very elastic and “stretchy”. This can lead to larger items, such as sheets and duvet covers, acquiring long curved creases in the centre during calendering.

Similarly, if the yarn thickness, which is measured in tex, is too high, the fabric will absorb more moisture and take longer to dry.

The next aspect that needs to be specified is the thread count, the number of yarns used per unit of measurement in both the warp and the weft. The higher the thread count the denser the fabric. The fabric is often described by the total thread count for both warp and weft. A cloth with 100 threads per inch in the warp and 125 in the weft would be a 225 thread count cloth.

Sheets and pillowslips will commonly be 200 – 250 thread count. Thread counts much higher than this reduce the fabric permeability, causing severe problems if the fabric is processed in a tunnel washer. A high thread count, say 300, will trap air in the fabric causing ballooning, which can lead to blockages in the tunnel. Larger items such as super-king duvet covers frequently burst in the membrane press when the hydraulic ram rapidly squeezes out the excess moisture (and air). High thread counts will increase the risk.

The fabric’s permeability is also affected by the type of fabric dressing that the manufacturer uses to enhance and assist in weaving.

The use of ultra-high-speed looms demands that the warp yarns are significantly stiffer and smoother to reduce the risk of breakages. Manufacturers used to use conventional starch, which is easily removed during the first wash process but more recently there has been a move to modified or synthetic starches, often containing polyvinyl acetate or a silicone, which take 10 –15 normal wash cycles to remove, sometimes longer.

These fabric dressings give the linen a much crisper finish but if they are not removed in the first wash, it will be difficult, if not impossible, to produce a well ironed sheet and the fabric will be covered with tight, short creases, often referred to as “cracked ice” creasing.

So the specification must state the permissible finishes or demand that finishes must either be completely removed before delivery or at least readily removable in the first wash.

After weaving, the material will go through a series of processes to whiten the fabric, to pre-shrink it and to heat-set the shape, (especially polyester-cotton blends).

Cotton is naturally creamy in colour but most users prefer a bright white look. So manufacturers will bleach the fabric and add optical brightening agents to enhance the whiteness. Any bleaching process will cause some fabric damage, the extent depends on the bleach type and the length of exposure to bleach.

For 100% cotton fabrics the degree of chemical damage is normally measured using the cuprammonium fluidity test.

This is not suitable for polyester or polyester blends so damage is assessed by a tear test either down warp or across the weft or by measuring the tensile strength.

The specification must include the maximum permissable damage otherwise it could fail halfway through the planned rental period.

Finally, the fabric should be correctly pre-shrunk. All textiles are woven under tension – which is released during the first 3 – 5 laundry cycles. Most modern fabrics will normally shrink by 5 - 7%, so the finished size should allow for the inevitable shrinkage and the specification should state the target finished size after five washes.

Several other factors should be included in the fabric spec but I will deal with these in a later article.

The key to textile purchasing is to know your requirements, specify these in detail and check each consignment/delivery to ensure it complies with your specification.

Some organisations now buy textiles directly from the mill to reduce costs. Most weaving mills are now in places such as Egypt, Pakistan or China and time differences and language barriers can make communications more difficult. More importantly, companies importing directly will have to pay in advance and if the goods do not meet the laundry’s spec, it can be problematic returning a 40ft container of textiles that has already been paid for. A UK distributor will often hold large quantities of stock and take responsibility for ensuring that orders meet specifications.