After doing some more research into the formaldehyde used in engineered wood products (MDF, particle board, OSB, etc) I’ve found out some useful information.

I work in the construction business and was always told the only real danger was during cutting and mostly so only in MDF. When I heard of MDF being dangerous for reptiles I was very curious. I’ve been asking around with other people that have had a lot more experience with wood products than I.

1.First off many people on here seem confused on engineered wood products.
There are several different types commonly used in making reptile enclosures.
Solid wood is typically the most expensive. Untreated wood can be found in a variety of sized, but becomes unrealistic after a certain width. Cost is also based on the number and size of knots in the wood.

It can be shaped and sanded with almost all wood tools. It can be stained, painted, or coated with most products. It is also one of the lightest materials by volume. Besides cost another downside is it is more likely to warp, expand and contract.
Plywood has at least one side with a solid wood veneer. The veneers are are made from a large log that has been peeled around the edge making thin, but wide pieces. These layers are pressed and glued with the grains facing at 90 degrees. Plywood comes in all types of wood veneers.

Only the outer facing edges are made from the hardwoods. For example your standard oak plywood has either pine, douglas fir, poplar or other fast growing tree as the core. Also hardwood plywood can come with particleboard or MDF core. Prices vary by number and size of knots and by how it is sanded. Plywood can be sanded to an extent and the veneer treated like solid wood for coverings.
OSB is short for Oriented Strand Board. This is made of large particles of wood chips positioned in overlapping directions then pressed and glued together.

This can’t be sanded and does not have a smooth surface when painted and is mostly used as underlayment.
Particleboard is made with smaller particle of softwoods that have been pressed and glued into sheets.

. Often this product is covered with melamine

. This accounts for the majority of melamine board found in hardware stores. This material is heavier than solid wood; however, it lacks grains so warping, expanding and contraction ore for the most part eliminated. Due to the size of particles it does not react well to sanding and shaping. Some downsides to particleboard are it is less structurally sound than wood, it does not paint as smooth, and the wood does not hold up to moisture well. The last problem is fixed when coated with melamine. There are several different processes for applying the melamine.
MDF or medium density fiber board is similiar to particleboard except the size of the particles used are significantly smaller (think cardboard fibers instead of large sawdust). The process of heating, pressing and gluing removes most of natural resins from softwoods that cause problems in reptiles.

This also can be covered in melamine

This is nowhere as near as common as particleboard cored melamine. It is heavier and more expensive. In North America this is typically a special order item and not stocked in hardware stores like Home Depot and Lowes. MDF gives off a very fine dust when cut or sanded and special precaution must be made as it irritates the eyes and respiratory system. It can be painted and shaped similiar to wood. It is heavier than particleboard and can split or crack when using screws.

2. The amount of formaldehyde in the glues
Particleboard and MDF are both indoor only products. They both react poorly when exposed to water. This is because of the glue used to hold the particles together. Formaldehyde is contained within these glues.
Urea-Formaldehyde is used in both these products and hardwood plywood. HCHO or formaldehyde is released from hydolysis or in simpler terms water breaks the glue into two parts, one being formaldehyde. So an introduction of water (liquid or vapor from humidity) without sealer not only can make the product expand/warp, but the glue breaks down releasing formaldehyde.

Solid woods obviously contain no type of formaldehyde so there is no worry there.

OSB and softwood plywood is glued with phenol-formaldehyde. These are made for outdoor use and can resist moisture much better. Phenol-formaldehyde releases about 1% the amount of emissions MDF historically does.

3. Formaldehyde limits by location In America formaldehyde emissions are limited to .3ppm (parts per million) California has formaldehyde emission free policy.
Germany seems to be the strictest county with .1ppm. Norway, Hungary and Australia also all have limitations. As far as I know the UK and China have no such restrictions.

4. Table
Product emissions (one millionth gram per square meter surface area per day)
MDF 17,600-55,000
Hardwood Plywood 1500-34,000
Particleboard 2000-25,000
Softwood Plywood 240-720
Fiberglass Products 400-470