See the Wikipedia article on Plywood for more. This article is centered around what's available in the United States and Seattle in particular.

Plywood is an essential building component at PKV. Most everything we build out of wood uses plywood in some way. Plywood comes in several different types and grades so it's good to educate yourself on what is available for your region before the start of a project.

Softwood Ply / Construction Ply

Construction rated plywood is what you'll hear the most referred to as ACX, CDX, etc. which is used in the construction industry for the insides of walls and underneath floors. The first two letters denote the quality (size of voids, patches, cracks, etc) of the front and back face with A being the best, D being the worst, and the X is short for the type of glue used (eXposure grade 1 gives it a bit of moisture resistance). This type of plywood is produced to a set standard of strength for use in construction and is fairly consistent.

Hardwood Ply

Hardwood ply comes in a variety of different grades and grading schemes depending on where it comes from and what it is used for. Hardwood ply can be purely an appearance based plywood with nice face veneers and particleboard/MDF inside for things like cabinetry or can be crazy strong 13 layered hardwood Baltic Birch/Appleply. Different brands and different stores can produce drastically different sheets so be sure you're inspecting and choosing your suppliers well1). The strongest hardwood plywoods are those that have high numbers of plys (layers) in-between the outside faces and where each of those layers is made of a hardwood species.

Parkour Visions Standards

PKV's favorite plywood for building parkour obstacles is 3/4“ Scuf Superply. Solid core under face (Scuf) is a softwood plywood which has less voids under the outside layers which helps to prevent cratering and Superply is a product that has nice patch-free hardwood veneers on the outside faces. We usually get this from Dunn Lumber at less than $60 per 4'x8' sheet. At the same price point there is also a softwood only void free ply called Hardel which has less voids present in the inner layers (making it stronger) but tends to have a much lower quality face than Superply (even at an A rating).

We haven't been able to find a 3/4” all hardwood ply around the same price but would likely use that instead if we could find it (especially if it was void free) since hardwood ply like baltic birch can be stronger, more impact resistant, and hold fasteners better than softwood ply.

The cheapest 3/4“ ply stock tends to be CDX which you can often find for $25 a sheet. Beware of using this in projects though as any exposed edges or faces tend to be break down easily, there can often be huge voids in the middle layers that won't hold fasteners, and the layers can delaminate with heavy use. We only use CDX for internal reinforcements for this reason as that is what it's designed for anyway. OSB plywood is in a similar boat where it can break down over time and flake off with impact - even if it's painted over.

It can be tempting to move down to 1/2” to save some money and/or weight but be aware that it is possible to blow through a 1/2“ plywood piece with heavy parkour use (even on 16” centers). More research needs to be done to see how much force is really needed for this but anecdotally 1/2“ has been broken through whereas 3/4” ACX or above plywood on 16“ centers has not. If you are going to go for 1/2” at least do your research to go for quality Scuf Superply or a hardwood like Birch.