BMT combines stretch blow moulding simulation and physical testing to assess the impact of altitude-induced pressure changes on lightweight bottle performance.

As packaging manufacturers continue to pursue lightweighting strategies, ensuring bottle performance throughout increasingly complex distribution networks remains a critical engineering challenge. A new study by BMT demonstrates how integrated simulation and physical testing can be used to predict and mitigate altitude-induced bottle deformation before products enter the supply chain.

Pressure differentials created when products filled at high-altitude facilities are transported to lower elevations can generate an internal vacuum effect within sealed containers, leading to deformation in the shape of panelling, and in severe cases, structural collapse. With altitude-induced pressure changes being a well-recognised consideration in package development, it can result in over-engineering and create conflict with bottle lightweighting aims.

To address this challenge, BMT developed an integrated engineering methodology combining stretch blow moulding (SBM) simulation and structural testing to assess the impact of fill volume on bottle performance under altitude-induced pressure changes. The approach was validated through a Mount Everest inspired case study simulating a bottle filled and sealed at the summit before being transported to sea level.

"Packaging performance must be assessed across the distribution chain, not just at the point of manufacture. This work demonstrates how simulation and physical testing can be used together to predict altitude-induced panelling and support more informed package design decisions" says Ross Blair, Head of Engineering at BMT.

The Everest scenario created a pressure differential of approximately 680 mbar between the summit of Mount Everest and sea level, enabling engineers to investigate the effects of altitude-induced loading on lightweight PET packaging. Advanced simulation techniques were used alongside physical pressure chamber testing to recreate the deformation and validate model predictions against physical test results.

The study also examined the impact of headspace volume on bottle performance. Bottles were filled to varying levels to assess how the volume of air above the liquid influenced deformation under vacuum conditions.     

Figure 2: Collapse pressure across different fill volumes

The results indicate a non-linear relationship between fill volume and the pressure required to initiate collapse, with increasing fill levels leading to a disproportionately higher vacuum pressure threshold. A fill volume of 97% delivered the best overall performance, minimising maximum sidewall deflection while limiting total bottle volume reduction to approximately 1.2%. Overall, the findings demonstrate that reducing headspace decreases deformation and significantly increases the pressure required to trigger structural collapse. This approach enables manufacturers to quantify the trade-off between increasing fill volume and reducing bottle weight. While higher fill volumes can improve performance, they may also increase product costs, helping teams identify the optimal balance between package performance and cost.

While increasing fill volume represents one route to improving performance, the findings also suggest that thickness distribution, SBM processing conditions and bottle structural design can play an important role in resistance to panelling.