Yes, UHMW polyethylene. The spring has steel bushings on each end and a rubber hose surrounding it. You can buy these plans for $35 (if I remember correctly) from Clay Spencer--- email- email@example.com Plans do have a copyright. I believe he will send you a printed set of plans or pdf file once the payment has been made. I opted for the pdf file. He also has tire hammer workshops. Raymond Head (on youtube) has the rights for making parts as well as completed hammers. I did buy a good number of parts off him. Both Clay and Raymond were great people to deal with and happy to answer any questions that I had.