I think you're passing querystring parameter while redirecting to another page.
Like if your textbox contains value of "glass" then are you sure you're redirecting like below ?
Response.Redirect("page.aspx?product=glass)
You will find glass in a second page like
string prod = Request.QueryString["product"].ToString();
Page redirection depends on the page hierarchy also, And further share your code to be clear the way you're currently doing the same.