The single most important thing in a boulder mat is the foam. It is the foam that absorbs the impact of falls. I've recently been learning more than is healthy about foam, with a view to improving and redesigning the boulder mat range. So, what makes the perfect bouldermat foam?
In theory the ideal foam for bouldering pads is a thick, soft, high density natural PU foam (think gymnastic crash pads/mats at climbing walls) which will absorb energy slowly giving softer falls, it will last longer and you’d get seriously buff carrying it to the crag. In reality the practicality of using such a pad means that a compromise has to be made; it doesn’t matter how good your pad is if you break your ankle because you couldn’t be arsed carrying it to the problem!
So, how should we go about choosing which foams to put in our mats, or even comparing pads that are already out there?
There seems to be lots of chatter about foam on forums, but the only comments are either ‘crap’ or ‘soft’ and nobody seems to have any basis for these opinions beyond anecdotal experiences, and the limited spec. info available from pad manufacturers make it difficult to assess these statements either way.
The foam’s density seems to be the only standard measurement anyone talks about (although few manufacturers actually quote it,) but this doesn’t tell us the whole story. In fact the foam used in nearly all mats has additives mixed in to make it artificially harder than it should be for a given density. This has the effect of making the pad lighter for a given hardness compared with using a ‘natural’ foam, but at the cost of durability. This is why the foam in your pads start to degrade and become soft after a couple of years’ use but the foam in your mattress (the same foam, fact fans) will last ten years or more.
Knowing the foam’s density does not automatically tell you how hard or soft a foam will be; high density foams can be produced to be very soft and vice versa. So why worry about density? Because several studies have successfully correlated the results results of flex fatigue tests on PU foams and all reach a similar conclusions; as polymer density increases hardness loss is lessened and hardness loss in fatigue testing happens early in the testing cycle with the majority of loss typically occurring within the first 1,000 test cycles. So higher density heavier foam may be heavier and costlier but it will last longer, and foam that is not up to the job will get soft, fast! How long do you think it takes to clock up a thousand falls on your mat? A few good weekends?
So perhaps the weight of a mat is a better judge of it's quality than it's hardness since a light, hard mat will be a light, soft mat in a few sessions time!
The surface hardness is another property we can measure, this what you can feel when you stand on a pad or squeeze in a shop and is a major contributor to the pad’s ‘softness’ sensation which is how most people currently seem to assess mats. In fact it is the deep down support which carries much of the load and will do the business on bigger falls, this can very different to and is not directly related to surface firmness; just because a mat feels ‘soft’ does not mean it will be more likely to bottom out, it will however definitely be much kinder to your body on smaller falls! It is not unusual for a soft foam to have higher support properties than its surface hardness would indicate. Foam with higher support (think deep down firmness) can be specified with softer surface hardness without sacrificing the ability of the foam to bear a load so while the foam can feel squishy and cushy for small falls, the force required to bottom it out is large, this obviously has interesting connotations for boulder mat design.
So where do we go from here? We reckon the ideal foam should be soft on small falls, but very resistant to bottoming out when you hit it from height. Higher density foam lasts longer so it makes sense to use the highest density foam we can within the limits of what users will be happy to lug around (and pay for!) We've got a pile of foam from our suppliers, (including one extremely pimp secret foam that Jim and I are very excited about, but I'd hate to spoil the surprise!) so the next stage is building a selection of prototype pads and getting jumping (as well as some slightly more scientific assessment,) so maybe we'll see you out there!