I can not save the material of a part (a userdata value) how do you solve that? [SOLVED]

function generateDataTable(player)
    local dataTable = {}
    for i,v in pairs(game.Workspace.TestFolder:GetChildren()) do
        table.insert(dataTable, (tostring(v.Position)..","..tostring(v.Color)..","..tostring(v.Material)..""))
    end
    return dataTable
end

Fixed thx to greatneil80