A lower price per kilogram of butyl compound does not necessarily mean a lower tape production cost. At the same width and thickness, material consumption also depends on density. Once losses, actual dimensions and line operation are taken into account, the ranking of quotations may differ from a comparison of purchase prices alone.

For B2B purchasing, it therefore makes sense to use a common basis for comparison: the cost of producing 1,000 metres of tape that meets the agreed requirements. This connects purchasing decisions with process performance and production profitability. The first step is to calculate the cost of the compound itself. The next is to establish the actual cost of converting it into a finished product.

Why price per kilogram is not enough to compare butyl compounds

A kilogram measures the mass of the material being purchased. Producing tape with a specified cross-section and length, however, requires a particular volume of compound. Two formulations can have different densities, so the same mass can produce different lengths of tape.

Industry guidance explains that the properties of butyl sealants depend on their formulation: a single set of parameters cannot be applied to the entire product group. Calculations must therefore use the density of the specific compound, rather than the density of butyl rubber alone. [1]

A useful intermediate measure is the cost per litre of compound. Since 1 g/cm³ is equivalent to 1 kg/l, multiplying the price per kilogram by the density in kg/l gives the cost per litre of compound. This shows the cost of the volume required to fill a given cross-section.

This does not mean that the compound with the lowest density should be selected. Its suitability must be assessed against the requirements of the finished tape. Density alone does not determine adhesion, durability or processing behaviour.

Start with a common tape specification

A reliable comparison of quotations starts by defining the product to be made from the compound. Agree the following for both options:

• the width and thickness of the butyl layer itself, including permissible tolerances;
• the type of carrier and release liner, where applicable;
• the substrates to which the tape must adhere and the application method;
• the required sealing performance, adhesion, temperature resistance and other properties relevant to the application;
• the test methods and acceptance criteria for the finished product.

Butyl product documentation lists peel adhesion, shear properties, density and water vapour transmission as separate properties, each with its own units and test methods. A claim of “high adhesion” alone is therefore insufficient to compare two materials. [2]

Solutions with different thicknesses can also be compared, provided they have been confirmed to meet the same performance requirements. In that case, each quotation must be calculated using its actual cross-section. Equal tape lengths do not necessarily represent equivalent products.

How to calculate compound cost per 1,000 metres of tape

For a uniform butyl layer with a rectangular cross-section, the calculation comes down to geometry and density. For a length of exactly 1,000 metres, the following simplified formulae apply:

In these formulae, M is the mass of compound per 1,000 m in kilograms, b is the layer width in millimetres, h is its thickness in millimetres, ρ is the density in g/cm³, and p is the price per kilogram. The result, K, is the cost of the compound alone per 1,000 m, excluding production losses.

At a width of 20 mm, a thickness of 1 mm and a density of 1.60 g/cm³, 32 kg of compound is therefore required per 1,000 metres of tape. The volume of this layer is 20 litres.

The formula requires the stated units and applies only to the butyl compound. The mass of aluminium foil, nonwoven fabric, release paper or a core is not part of the compound mass. For profiles of a different shape, use the actual cross-sectional area instead of width multiplied by thickness.

Worked example comparing two butyl compounds

Assume that the tape has a butyl layer 20 mm wide and 1 mm thick. In this example, both compounds are assumed to meet the same performance requirements.

The data in this example is hypothetical. We assume a price per kilogram of 1.60 for compound A and 2.00 for compound B. All prices and costs are expressed in the same arbitrary unit. The comparison assumes identical delivery terms.

The compound cost per 1,000 m is 32 × 1.60 = 51.20 for A and 25 × 2.00 = 50.00 for B. Compound B is 25% more expensive per kilogram, but the cost of the butyl required for 1,000 metres of tape is 1.20 lower, or approximately 2.34% less than for compound A. This is because less mass is required to obtain the same layer volume.

With the same dimensions and the same loss rate, the material cost of the two options becomes equal when B is priced at 2.048 per kilogram. This follows from: 1.60 × 1.60 ÷ 1.25 = 2.048. At that price, the cost of B per 1,000 m is 25 × 2.048 = 51.20. Above this price, B loses its advantage in compound cost alone, provided all other assumptions remain unchanged.

The result also depends on the actual thickness. If the average butyl thickness applied is 1.10 mm instead of 1.00 mm, at the same width, consumption increases by 10%. It is therefore useful to compare the nominal dimension in the order with measurements of the finished layer and the butyl mass per metre.

How to account for production losses and material recovery

The geometric calculation shows how much compound is contained in correctly manufactured tape. Actual consumption must also include material used during start-up, cleaning and changeovers, as well as material in products that do not meet the requirements.

If irrecoverable losses amount to 5% of the input mass, 95% of the compound fed into the process remains in conforming product. The required mass must therefore be divided by 0.95. For the example in the table, this gives:

• compound A: 32 kg ÷ 0.95 = approximately 684 kg of input per 1,000 m; cost: (32 ÷ 0.95) × 1.60 = approximately 53.89;
• compound B: 25 kg ÷ 0.95 = approximately 316 kg of input per 1,000 m; cost: (25 ÷ 0.95) × 2.00 = approximately 52.63.

For both options, compound cost increases by approximately 5.3% compared with the calculation excluding losses. Multiplying the mass by 1.05 would represent a different calculation: adding 5% of the mass of good product. When comparing quotations, clearly define the basis of the loss percentage. If loss rates differ between compounds, use the individual rate for each.

Material that is actually recovered and reused must be accounted for so that it is not repeatedly counted as new consumption. Reprocessing can, however, generate labour, energy and machine-time costs. If actual consumption already includes waste, do not add the value of the same lost compound again under the cost of rejects.

From compound cost to total tape production cost

The costs of 51.20 and 50.00 in the table relate only to the compound. They are neither the tape selling price nor its full manufacturing cost. A production comparison must also include the following costs per 1,000 metres of conforming product:

• carrier, release liner, cores and packaging;
• energy, operator labour and equipment operation;
• start-ups, changeovers, cleaning and downtime;
• quality control, rework and customer complaints, where data allows these costs to be reliably allocated.

Use a consistent costing method. If the hourly line rate already includes energy and labour, do not add those items again. Compare purchase costs on a common basis, treating transport, packaging and discounts consistently.

Compound yield in metres per kilogram and line throughput in metres per hour are two different measures. Both affect costs. A material with lower mass consumption may require more processing time; the size of that effect should be established through a trial rather than assumed.

How to compare compounds in a production trial

A useful trial provides data for the purchasing decision. Simply proving that a compound can be extruded is not enough to assess its cost-effectiveness. Use the following procedure:

1. Define a common product and acceptance criteria. Specify the cross-section, tolerances, substrates and performance requirements. Confirm material suitability on the actual substrates and under the intended conditions, particularly for adhesion and compatibility. [3]
2. Record the line operating conditions. Note temperatures, speed, equipment settings and batch size. Use appropriate settings for each compound in line with the supplier’s recommendations; identical settings do not always produce a fair comparison.
3. Measure the actual product. Check the width, thickness and mass per metre of the butyl layer itself. Record variability as well, so that an average does not conceal sections outside tolerance.
4. Reconcile material consumption. Include input, waste, recovered material and material remaining in equipment or work in progress. Compare batches after reconciling opening and closing balances.
5. Count the length of tape that meets the requirements. Include only sections that meet the agreed criteria. Also record the total trial duration, start-up time and downtime.
6. Convert the result to a basis of 1,000 metres. Divide net compound consumption in kilograms by the length of conforming tape in metres, then multiply by 1,000. Multiply this figure by the price per kilogram and add the other allocated costs.

Net consumption defined in this way includes the material in good product and actual losses, adjusted for returns and inventory changes. It shows whether the advantage identified in the calculation holds under production conditions.

What information to request from a butyl compound supplier

A request for quotation is more useful when it covers the following in addition to the price per kilogram:

• compound density, its tolerance, and the measurement method and conditions;
• a technical data sheet with test methods and a distinction between typical and guaranteed values;
• processing recommendations for the type of equipment used;
• storage requirements and shelf life;
• supply format, minimum order quantity, lead time and complete pricing terms;
• the availability of material for trials and the method used to verify batch consistency.

Assess the quotation together with a process technologist and the person responsible for quality. The best purchase is the compound that delivers the required product at the lowest substantiated total cost.

Planning to purchase a butyl compound? Prepare the target tape dimensions, performance requirements and expected production volume. Ask the supplier for calculation data and the terms for running a trial. Include the cost per 1,000 metres of specification-compliant product when comparing quotations.

Frequently asked questions about butyl compound prices and yield

Can a more expensive butyl compound reduce tape production costs?

Yes. A higher price per kilogram can be offset by lower material consumption or a more efficient production process. The final result depends on density, actual cross-section, losses and other costs. The comparison must concern tapes that meet the same requirements.

How many metres of tape can one kilogram of compound produce?

It depends on width, thickness and density. In the example above, with a layer measuring 20 × 1 mm, one kilogram of compound at a density of 1.60 g/cm³ theoretically produces 31.25 m of tape; at 1.25 g/cm³, it produces 40 m. These figures exclude losses.

Does a lower compound density mean higher quality?

No. Density is used to convert mass into volume and consumption. Assessing quality requires separate confirmation of performance properties, process stability and supply consistency. Product composition or durability cannot be inferred from density alone.

Can the cost per 1,000 metres be compared for tapes of different thicknesses?

Yes, once both solutions have been confirmed to meet the requirements of the same application. Use the actual dimensions and production results for each option. Reducing thickness without checking tape performance does not establish a cost saving for an equivalent product.