So, you might need to clarify your question,
Kelcat , as Galactic Armory sells 3D Print Files for ODSTs, but they have also partnered with Sean Bradley to sell his Vacuum Form ODST armor kits.
If you're getting the Sean Bradley Studios ODST armor kit, the most common method of reinforcing it was to add a layer of Fiberglass to the inside of the pieces. This was done because the plastic Sean used to pull his kits back in the day was relatively thin and prone to cracking or tearing at the edges. I have not spoken to anyone who has purchased the kit from Galactic Armory, so I'm not sure if the same level of plastic is being used by GA that Sean used to used, or if they have upgraded to a different or thicker plastic. If you do a search ere on the Forum for "Sean Bradley ODST Kit" you should have many, many Work In Progress or build threads of members putting together their kits from Sean that can show you how they reinforced their kits.