A 3D printing kit can include a powder bed material comprising from about 80 wt % to 100 wt % polymer particles, a fusing agent to selectively apply to the powder bed material, and a hardener to selectively apply to the powder bed material. The polymeric particles can include a polyalkylene backbone with both ethylene and propylene polymerized monomeric units with from 2 mol % to 15 mol % of the polymerized monomeric units include a grafted side chain having an epoxide moiety. The fusing agent can include water and a radiation absorber that absorbs electromagnetic energy and converts the electromagnetic energy to heat. The hardener can be present in the fusing agent or can be included in a hardening agent that is separate from the fusing agent.