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Carbon footprint benchmarks

Learn how Sourceful calculates carbon footprint benchmarks for products like mailer box, shipping box and tape.

Last updated: Mar 18th, 2022


At Sourceful we value transparency, this is why we’ve measured and published the full carbon footprint results for each of our products. It’s also why we’ve verified our life cycle assessment methodology to ISO 14040 and 14044.

However, seeing a carbon footprint number in isolation means it’s hard to know the significance of that result. The solution we’ve therefore provided is to show you an indication of the environmental value Sourceful could be providing versus what is commonly seen for a given product. This is calculated under a comparable set of assumptions.

How we calculate our benchmarks

Sourceful’s benchmarks are based on the idea of running scenarios on our LCA models, built using a consistent ISO-conformant methodology. As such, we are able to maintain the same LCA modelling approach. This means we keep the same system boundaries, data quality checks and calculation methods for all the variants.

Below you’ll find information on the specific assumptions used to develop the benchmark for each of our products.

Mailer box


A study from DHL in 2020 [1] found that, on average, boxes used for shipping items have 40% of void space. This excess of material is an avoidable environmental impact, that can be reduced via custom sizing.

We wanted to understand the impact of being able to right-size your box. We assumed that you’d be able to reduce the void space to 20% as a result of custom sizing.

The second component of our benchmark is sampling. In the corrugated box industry, sampling, especially blank sampling, is commonplace. Based on our experience, we have assumed a typical case where a business will receive three blank mailer box samples to test the exact sizing and functionality of the box. Additionally for mailer boxes where printing is required, we have assumed a case where a business will pay for two printed samples to visualise and sign-off their artwork. These assumptions are conservative estimates based on our experience of sourcing mailer boxes for our clients and advice received from our domestic and international manufacturers. With Sourceful’s online platform, thanks to our 3D design studio where you can visualise the artwork you apply to your product, no sampling is assumed to be required.

For international suppliers, these samples are air freighted, whilst for UK suppliers they are delivered via normal road courier. We validated the assumption with our suppliers that even a small sample run will require the same print setup, and that samples are couriered.

Sourceful’s 3D design studio platform allows you to visualise the artwork you apply to your product. We assume that you can use this feature to eliminate the need for, and impact of, these rounds of sampling.

Finally, given the challenge to source high-quality, affordable offset print in the UK, our benchmark assumes the boxes are sourced from international suppliers.

When further comparing the premium mailer box to the eco mailer box, we took an average across a range of order quantities, printing, and sizes. Premium boxes were assumed to be transported by sea freight.

The benchmark is defined as the sum of the carbon footprint for the larger boxes and for both sampling rounds:

Paper mailer bag

The benchmark for the paper mailer bag is based on a comparison to a common plastic alternative, an un-gusseted LDPE mailer, to estimate the difference in carbon footprint between the two options.


To ensure that we were producing a fair and accurate comparison between the two products, aligning to Life Cycle Assessment best practice, we normalised the carbon footprint results of both products by ensuring they delivered the same function. Specifically, we normalised the results using a measure of the amount of product the two bags can package, i.e. their usable packing volume[1]. To determine this, we measured their usable volumes using loose tea leaves.

To ensure the comparison between the two products was consistent and focused on the materials, we assumed the same supplier manufacturing location. The product we modelled was a mailer bag with single peel and seal, 1 colour printing, for a 1000 units order quantity.

The LDPE mailer benchmark footprint was based on information from one of our current 98% recycled-LDPE mailer producers, who also produces a virgin-LDPE mailer for other clients.

The key differences between the products in this comparison are the thickness and weight of material needed (LDPE is around half of paper, given different densities and strength), print technique (LDPE is flexo vs. digital for paper), disposal (recycling rate is just 6% for LDPE in UK vs. 74% for paper). There are also differences in the production steps needed to produce LDPE film vs. paper, and given their difference in thickness, in the way they are packed before being shipped.

The benchmark is defined as the carbon footprint of an LDPE mailer, which is compared to that of the paper mailer:


[1] Useable volume: The usable volume of a mailer bag refers to the maximum amount of space inside the bag that can be used for packing and shipping items while still allowing the flaps of the bag to close comfortably, without putting undue stress on the bag or items inside.

Shipping box


The benchmark for shipping boxes follows the same logic applied to mailer boxes on void space, given we also offer custom sizing for our shipping boxes.

Sampling is handled differently though. Rarely will you run a printed sample for a shipping box, instead you may have 1-2 blank samples. Given this would have a negligible impact, we have not assumed sampling in the benchmark.

The benchmark is defined as the carbon footprint of non-custom size boxes:

The benchmark for shipping boxes was calculated following the same approach used for mailer boxes, excluding the impact from sampling.

Recycled Mailer Bag

The benchmark for the recycled mailer bag focuses exclusively on the recycled content of the plastic film. In turn, it gives an indication of how important it is to move away from virgin plastic.


Our supplier manufactures mailer bags with 0% recycled content, as well as the 98% and 30% recycled mailers that we offer. This means to calculate the benchmark, we were able to use the same manufacturing, secondary packaging, transport and end of life assumptions for all products. We then changed the dataset used to model the film. As a result, we can show the potential difference in your carbon footprint when you order a 0%, 30% and 98% recycled content mailer bag.

Tape (gummed and self adhesive)

Screening the market, PVC (Polyvinyl Chloride) and BOPP (Biaxially Oriented PolyPropylene Films) tapes represent the vast majority of alternatives to paper-based tapes. Custom printed paper and plastic tapes, whilst possessing quite different properties, have very similar applications.

For tapes, we calculate a benchmark of both a PVC and a BOPP tape. We do this by taking the carbon footprint model of the paper-based tapes, and running a scenario to replace the base material, adhesive and end of life scenario. By doing this we can understand the potential impacts of moving from plastic-based to paper-based tape.

The benchmark is defined simply as the carbon footprint estimate of the plastic tape:


Our lead supplier for gummed and self adhesive tape also produces PVC and BOPP tapes. They confirmed that the assembly process (printing, cutting and rewinding) is operated on the same machines. Hence, we kept the manufacturing and the transport components the same.

Based on their information, we made changes to three areas:

  1. Amount of material
    Given that our lead supplier for paper tapes also produces PVC tapes, we used their GSM (grams per square meter of material) for PVC tape. For BOPP, we assumed the thickness based on literature [2] and calculated the GSM using an average density. A market analysis further validated our assumptions on the amount of material used in PVC and BOPP tapes.
  2. Material datasets
    In keeping with the method for paper tapes, we used industry average emission factors from ecoinvent (an internationally recognised LCA database) to represent PVC and BOPP granulates and the subsequent extrusion process to obtain films.

    From our supplier, we found that plastic tapes tend to have different types of adhesives (commonly a natural rubber adhesive). Using literature ([2], [3]), we modelled the composition of the new adhesive by selecting the following components: natural rubber and hydrocarbon resin.
  3. End-of-life scenarios
    To be consistent with our LCA methodology, if materials cannot be recycled and there is uncertainty whether they end up in incineration or landfill, we take the worst-case scenario. This means for PVC and BOPP tapes, we assume they are 100% incinerated at end of life. For self adhesive tape, we know it cannot be easily recycled; paper performs much worse in landfill than incineration, hence we assume 100% is landfilled. Gummed tape on the other hand can be recycled, therefore we assume the UK average allocation for paper across recycling, incineration and landfill [4],[5].

We calculated the carbon footprint for over 50 variants of each of the Sourceful tapes, and for each of the BOPP and PVC tapes. We normalised these to m^2 to provide a common basis for this analysis. We then estimated the average footprint for each type of tape, to identify the indicative differences between the Sourceful product and the benchmark.


Our assumptions are made in line with our LCA methodology and validated by product suppliers and peer-reviewed studies. However, there are some limitations to the use of these benchmarks, which we will continue to address and improve in our method.

  1. We have no control over the end of life of the products, and in-turn have little to no visibility into UK averages for where products like tapes might end up. To mitigate this risk we assume the worst-case scenario as per our methodology. This is unlikely to exactly reflect reality, given waste disposal is not so straightforward.
  2. Our LCA methodology focuses only on global warming impact. Assessing environmental impact through a single impact category could lead to omitting consideration for other important environmental risks. For example, the global warming impact cannot account for the impact of microplastics, as well as the non-degradability of products in the environment.
  3. 20% void space is an assumption chosen for Sourceful custom-sized boxes. In reality, the impact of custom sizing could be higher or lower. We are simply estimating the potential impact, not the definitive impact. We will continue to monitor what we see with our customers and will refine our assumptions accordingly.
  4. For each benchmark calculation, we kept the manufacturing, supplier locations and transport components the same. This is a simplification to focus the analysis on the question or material at hand, however, it is unlikely to be the case in reality.

Sourceful’s LCA methodology is designed to provide best efforts carbon footprint estimates of our products. It’s not intended to be used for definitive comparative assertions but instead, to be used to illustrate indicative differences. This applies to all CO2e estimates of Sourceful products on the platform.


[1] DHL Trend Research, 2020. The logistics trend radar, 5th edition. Available from:

[2] Navajas, A., Bernarte, A., Arzamendi, G. et al., 2014. Ecodesign of PVC packing tape using life cycle assessment. Int J Life Cycle Assess 19, 218–230.

[3] Mohd Z., 2009. Approaches towards sustainability in midstream and downstream rubber industry: life cycle assessment (LCA) and environmental labeling. In: Seminar on Sustainability of Rubber Industry, MICCOS, Malaysia

[4] Eurostat, 2022. Recycling rates of packaging waste for monitoring compliance with policy targets, by type of packaging. Paper and cardboard packaging, United Kingdom (2018). Available from:

[5] Chartered Institution of Wastes Management. 2022. Incineration. [online]. Available from: