Foam type and source for straps and belts?

You could always use a sleeping pad. Yoga mats are heavy aren’t they?

Shoulder straps: 1/4″ closed cell foam used for lining automobile tops. 1/8″ closed cell foam used under hardwood floors. For applications needing more padding, sleeping pads work pretty well.

I personally use neoprene foam for packs and I couldn’t tell you about its recycled content or lack thereof. If the yoga mats are made from recycled/reclaimed material then go for it. Something that might be worth looking into are recycled foam carpet pads. They come in all sorts of thicknesses starting at 1/8″. Most are made from open cell foam scraps so would need to be sealed in some way, but if your intent on a recycled product they might be worth a look. I have no idea how well this material would actually function in real world use, but it’s an idea.

Just curious what kind of foams you’re using for backpack shoulder straps, framesheets, and hipbelts

Closed cell EVA or PE. Minimum of EVA 40 or PE 40 – the lighter stuff fails under load. Open cell is useless. Reconstituted foam is poor quality – more glue line than foam. Neoprene is very high quality, but expensive. The really light stuff is a bit fragile.