UKC

I have built my 2 year old son an indoor climbing wall in his bedroom and I'm looking for a suitable crash mat that won't cost the earth.

I considered using our old memory foam mattress, cutting it in half so it's double thickness and having it professionally upholstered but I'm not sure if the foam is suitable.

Although the wall is only 2.5 metres high and he won't be anywhere near the top for a while, I don't want to risk breaking bones for the sake of a couple hundred quid if a memory foam mattress is a definite no go 

Nothing is going to make it totally safe or eliminate the risk of broken bones. For reference, my Moon bouldering mat is about 3 inches thick and has two layers of differing density foam (a harder/firmer foam on the landing side). That has stopped me from 12 feet... not sure I'd totally want to totally wipe out on it though. As for your suggestion... try dropping something of a similar size and weight from a suitable height to make sure it doesn't bottom out. However, bouldering mats are designed to do the job. I'd say also say there are probably far more dangerous hazards in the vicinity to consider than just the floor... units, toys, etc.

Thank you for your advice I've made sure in the design that there's nothing near the climbing wall so hopefully that will eliminate any other potential hazards.

In the 80s, old mattresses were used for home walls

I’ve got one of these: 

https://www.continentalsports.co.uk/safety-mat-crash-mat

Expensive, but great quality. Smaller sizes are cheaper. 

'Sprung' mattresses can be a very poor choice, as sometimes they offer little resistance to a localised weight, as they're designed for lying on rather than for standing or jumping on. Foam mattresses are usually much better, as long as the foam isn't too soft. I have a fairly extensive home wall padded with a variety of foam mattresses. As long as there are two layers of them - partly for added absorption and partly to make sure no gaps can easily appear between them - then there's rarely any chance of a problem.

I had 4 old mattresses (sprung) topped with old carpet & rug, which worked well for my home wall years ago, though it was only 8' high.

Another vote for a carpet on top of the mattress/es to spread the load and cover any gaps.