"经过弹性处理的" can be translated into English as "elastically treated" or "treated for elasticity", depending on the context.
"Elastically treated" is more concise and directly conveys the idea that something has been processed to achieve elasticity.
"Treated for elasticity" is slightly more descriptive, emphasizing the purpose of the treatment.
In most cases, "elastically treated" would be a suitable and natural choice.