About 10 years after I left university, I went to a reunion of my former classmates. When we talked about our jobs, they were stunned when I told them I was still doing physics pretty much every day. “But I thought you worked on baby nappies!” I confirmed this was accurate, but added that I had just hired a theoretical physicist to help me develop the differential equations for urine transport through nappies.

My classmates thought I was being funny, but I was just telling the truth. I work in the research and development (R&D) division at Procter & Gamble (P&G) and we joke that what we do is not rocket science – it’s harder. The fact is that many commercially available software codes for simulating fluid flow and mechanics do not readily work for nappies. As a result, we continuously face situations where either the theory that describes relevant phenomena does not exist or the simulations are numerically unstable owing to challenges that are specific to our systems.

For example, unlike in geological materials, where the pore structure is typically relatively stable during fluid flow, the materials used for consumer products such as nappies are soft and can deform because of wet collapse or external conditions. In addition, the swelling of super-absorbent materials produces large changes in the dimensions of the pore structure. This poses a range of challenges when developing methods of physically characterizing the materials and theories of how they behave. In short, the stereotypical view that “consumer products are simple to use – therefore they are simple to understand” is almost completely wrong. After 23 years “in baby diapers” (as the Americans would phrase it), I still find myself using physics every day and having a lot of fun too.

An accidental entry

Joining P&G was one of the best decisions of my life, but it happened more or less by chance. I studied physics at the University of Leipzig in what was then East Germany and my diploma thesis focused on developing simulations to compute the molecular orientation of nematic liquid crystals in electrical fields. For my PhD, I extended these simulations to include birefringent optics, making it possible to predict the behaviour of liquid-crystal displays based on the display’s design and material properties.

When I graduated in 1991, I was only 26 years old, but I had met my wife at university and (as was common in East Germany at the time) we decided to have children early. Our daughter was born before I earned my diploma and our son a few years later. My original plan was to stay at university as an assistant after my PhD, working my way towards a tenured professorship. However, while I was working on my thesis the Berlin wall came down and after Germany reunited the university system changed almost overnight. Permanent assistant positions like the one I had hoped for were no longer available; instead, it became common to accept temporary assistant or postdoc positions, with the hope of eventually becoming a professor.

I decided that this new path would be irresponsible for our family and that working in industry would provide a safer and more stable environment. Then I spotted an advertisement in a newspaper; a company called Procter & Gamble was soliciting applications from graduate students to attend a seminar for “technical management”. I thought P&G must be a consulting company (it was unknown in East Germany and this was before the Internet became popular) and I had no idea what technical management was, but I was curious, so I sent in my application.

A couple of weeks later I received an invitation to an interview. When I arrived, the recruiter informed me that P&G was a consumer-goods company and that I would be interviewed for an actual job, since I was already too advanced for the seminar. I didn’t know any more about consumer goods than I did about technical management, but again, I was willing to find out and later that day I was offered a starting position in material development for Pampers, P&G’s brand of nappies.

A physicist among chemists

My first assignment at P&G’s centre in Schwalbach, Germany, was to develop an upgrade for the absorbent gelling material (AGM) in nappies that absorbs and “locks in” urine to keep the baby’s skin dry. AGMs are hydrogels that are made of partially neutralized polyacrylate polymer networks and they were originally invented for agriculture as a means of improving the water-holding capacity of soil. P&G had introduced AGMs into Pampers in the mid-1980s and now my boss was convinced that they could be improved.

AGM development was seen as the domain of chemists, and as the only physicist working on it within P&G and our material suppliers, I was really pushed out of my comfort zone. I had to learn a lot more about polymer chemistry and materials science. But I was also able to ask physics questions such as “How does liquid transport happen in nappies?” and “How can we understand how the swelling of the AGM changes this?” A few of these things were known qualitatively, but to my surprise there was no detailed understanding and no predictive model to guide me. I had to develop models and characterization-test methods on my own and the breadth of the task – which also included working with material suppliers and even supervising some consumer testing – was very new to me. However, I found it exciting and within a few years I led the first AGM upgrade in P&G’s European Pampers plants.

This success encouraged me to push my role as a physicist further. In addition to AGM development, I started programmes aimed at improving absorbent-core technology, and our modelling and simulation programmes. In a way, I think that being a physicist among non-physicists was one of the reasons for my success because my different point of view helped spur us along.

Becoming an ‘expert generalist’

P&G has a dual career system, with management and technologist tracks. I went for the latter, progressing from principal scientist in 1995 to research fellow in 1999. In 2006 I was inducted into the company’s Victor Mills Society, which is the top rung of the technical career track. In fact, it is a bit like being a professor because I get to lead major R&D programmes and help develop new ways of educating and nurturing young innovators. I also collaborate with a range of companies, universities and institutions, and frequently present at conferences.

The term “expert” is usually associated with deep knowledge in one particular field. However, I find it more useful to view myself as an “expert generalist” or “master integrator” – someone with deeper-than-average knowledge and experience of multiple fields. My physics education taught me that “if it is the same equation, then it is the same problem”, and I think this has helped me to think and act like a master integrator because I can find connections between areas that appear unrelated on the surface. This is especially useful at the fuzzy front end of innovation, when the uncertainties surrounding what is needed and what is possible are both very high.

One thing that my physics education did not teach me, however, was the role of emotions and perceptions in the decision-making process. When I started working at P&G, one of the first things I learned was that “perception is reality” for consumers; a product may work fine, but if it does not look that way, consumers will not accept it. It took me much longer to learn that “perception is reality” also applies much more generally in decision making. For example, I sometimes give a talk called “Can I trust your model?” that highlights the challenges of status-quo bias and human behaviour as it applies to innovation. Learning more about how to influence people has become a hobby for me, so I read a lot of books about behavioural science in addition to keeping up with new topics in physics, chemistry, materials science and engineering.

Overall, I have found that working as a technical expert at P&G has given me plenty of new insights, as well as tremendous opportunities for learning. I enjoy tasks that take me outside my comfort zone and being “in nappies” means there is also the sense of excitement that comes with getting new technologies into consumers’ hands – and onto the bottoms of their babies.