Ken Kozicki from our BISCO division recently led a discussion with one of our resellers, the Grogan Group (based in Australia), that highlighted some key design considerations for engineers when it comes to choosing seat cushion materials in rail cars. Ken highlighted the differences between Rogers MF-1 silicone foam for seat cushions vs. typical molded polyurethane cushions and their advantages for rail and transit authorities.  Fortunately the discussion was videotaped (thanks to the folks at Grogan Group!) and you can watch it at your leisure.   However we wanted to capture some of the key points Ken made during his talk.  He shared that while silicone foam is a bit more expensive than polyurethane materials, there are some intangibles that need to be considered:

About Molded Polyurethane Seating

Typical seating cushions in rail cars are a molded polyurethane that has a low performing compressibility rate when it comes to cushion comfort.  What this means is that a polyurethane seat wears out quicker over time, and it loses its “spring-back” force that helps make the seat comfortable.  Over time the foam actually shrinks and flattens out, the upholstered material covering the cushion stretches out, gets loose, and the seat’s comfort declines as more passengers sit on it.  This material also needs to be treated with fire retardant chemicals, which adds to the production cost.

About Silicone Foam

The production of silicone foam is a more sensitive process than polyurethane.  There are precise control factors that come into play when manufacturing silicone foam because it creates a chemical reaction, and if the recipe is slightly off or there is added humidity or temperature changes, it can change the nature of the end product and be out of spec ranges.  This complex process tends to keep the price higher than polyurethane when comparing the two materials side by side.

But on the flip side, silicone foam has many advantages that polyurethane does not.  It will not lose its “spring-back” force, and does not require fire retardant treatment.  And, the issues that happen with molded polyurethane don’t happen here:  the upholstery doesn’t loosen, the seat does not lose shape from long wear and the cushion does not shrink in height.  As a result, the life of a silicone foam seat cushion is much longer (getting back to those intangible benefits).  There is also less repair and refurbishment costs for a transit authority (and these are very tangible benefits).

To learn more about Rogers MF-1 Silicone Foam and how it provides better, long-lasting comfort in rail car seating, sit back and watch the video:

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Ken Kozicki from BISCO® Silicones recently authored an article for Railway Technology International about the design considerations that go into creating comfortable railcar seat cushions.  How important are first impressions for seating when a passenger steps into the railcar? Obviously, if it’s the Orient Express or another high end rail system, the feeling of luxury must be present.  But even for standard commuter railcars, seat cushions do make an impression.  Ken notes:

“…the most prevalent and obvious fixture within any interior, rendering, brochure, or maze of booth exhibits is the seat or array of seats. The type of seat will vary from the most outrageously luxurious – slated for a VIP very high speed Oriental Express pod – to the simplest and ergonomic that allows for rows and rows of passengers in a configuration that would be suitable for the rush hour of London, Shanghai or San Paulo….What has taken teams of engineers and designers months, if not years, to conceptualise, design, prototype, test (and re-test), will be given a judgment in less than ten seconds. So from that, one could wonder just how important is the first impression of a railcar seat?”

In this article, Ken look at the design considerations that need to be factored in when choosing the right seat cushion for a railcar:  Ken highlights the following:

  • the number of seating positions per coach (as required by the transit authority)
  • materials’ standards for flame, smoke, and toxicity (FST)
  • type of train service (urban metro system versus suburban commuter), and
  • severity of usage.

Ken also discusses the new concerns of sustainability and end-of-life:

“This is being driven by questions related to the disposal of the seat: “What will become of a worn, damaged, or obsolete seat?” Will it be thrown into a land-fill? What are the decomposition ramifications of that seat in a land-fill?”

All good questions.  But what about the seat itself and the cushioning material? Are some better than others?  Ken suggests yes, there are differences between one cushioning material from another:

“…cushions have differences in profile, appearance and texture, it is not obvious that there are different types of materials used to fabricate the cushions. These materials are usually in the form of foam, such as a filled-polyurethane, silicone, and melamine. The foam which is specified for the fabrication of the cushion will have been tested to the various FST standards, ensuring the safety of the passengers. In addition, some of the foam materials may have been cycletested to simulate wear and usage, which brings us back to our earlier statement of first impressions. Often, seat cushion foam materials are tested and certified to a characteristic known as indention force deflection (IFD).”

2-D & 3-D view of thin profile seat with loaded urethane

“A typical IFD test method will be comprised of a disk of a determined diameter that compresses the foam material a certain percentage of its thickness, and then measures the amount of “pushback” force the foam has. This is its indention force deflection, and is directly related to the comfort of the seat. In production, the foam will be certified according to this test. If it is within the IFD tolerance range, the foam will be qualified for seat cushion fabrication.”

Of course, Ken highlights that the bigger test happens after many months of wear on the cushion, after the “pushback” force has been worn down.  Different materials, like silicone foam, do a better job over the life of a cushion than other materials.

To read Ken’s final recommendations, either view the article here (in a magazine viewer) or download a full PDF of the printed article.

Related Links

BISCO Material Selection Guide

Floating Floor Design Tool